Move names of editors followed by (Ed./Eds.) and a comma before title in biblatex

Shameless plug: The styles of the biblatex-ext bundle have a slightly more sophisticated version of this implemented as an option. Load ext-<standardstyle>, e.g. ext-authoryear-comp and set the option innamebeforetitle to true.

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[backend=biber,
  style=ext-authoryear, innamebeforetitle=true]{biblatex}

\DeclareFieldFormat{editortype}{\mkbibparens{#1}}
\DeclareDelimFormat{editortypedelim}{\addspace}

\DeclareFieldAlias{translatortype}{editortype}
\DeclareDelimAlias{translatortypedelim}{editortypedelim}

\addbibresource{biblatex-examples.bib}

\begin{document}
\cite{sigfridsson,gaonkar:in,westfahl:space,vizedom:related}
\printbibliography
\end{document}

This is really where biblatex is not that flexible.

We can use xpatch to patch the drivers for @inbook, @incollection and @inproceedings

\xpatchbibdriver{inbook}
  {\usebibmacro{in:}%
   \usebibmacro{bybookauthor}%
   \newunit\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{bybookauthor}%
   \newunit\newblock
   \usebibmacro{byeditor:in}%
   \newunit\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {}{}

\xpatchbibdriver{incollection}
  {\usebibmacro{in:}%
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{byeditor:in}%
   \setunit{\labelnamepunct}\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor}}
  {}{}

\xpatchbibdriver{inproceedings}
  {\usebibmacro{in:}%
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{event+venue+date}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{byeditor:in}%
   \setunit{\labelnamepunct}\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{event+venue+date}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {}{}

We also redefine byeditor:in

\newbibmacro*{byeditor:in}{%
  \ifnameundef{editor}
    {}
    {\printnames[editorin]{editor}%
     \addspace\bibsentence%
     \mkbibparens{\usebibmacro{editorstrg}}%
     \clearname{editor}%
     \printunit{\addcomma\space}}}

and a new name format

\DeclareNameAlias{editorin}{first-last}

MWE

\documentclass{article}
\usepackage{xpatch}
\usepackage[style = authoryear-comp, maxnames = 99]{biblatex}

\renewcommand*{\finalnamedelim}{\addspace\&\space}
\renewcommand*{\intitlepunct}{\space}
\DeclareFieldFormat[article, incollection, unpublished]{pages}{#1}
\DeclareFieldFormat[article, incollection, unpublished]{title}{#1}
\renewcommand{\bibpagespunct}{\ifentrytype{article}{\addcolon}{\addperiod\addspace}}

\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@incollection{lennon1965,
  author    = {John Lennon},
  booktitle = {A book with articles},
  editor    = {Paul McCartney and John Lennon and George Harrison and Richard Starkey},
  title     = {This is my article in this book},
  year      = {1965},
  location  = {Liverpool},
  pages     = {65--87},
  publisher = {Cavern Club},
}
\end{filecontents*}
\addbibresource{\jobname.bib}

\DeclareNameAlias{editorin}{first-last}

\newbibmacro*{byeditor:in}{%
  \ifnameundef{editor}
    {}
    {\printnames[editorin]{editor}%
     \addspace\bibsentence%
     \mkbibparens{\usebibmacro{editorstrg}}%
     \clearname{editor}%
     \printunit{\addcomma\space}}}

\xpatchbibdriver{inbook}
  {\usebibmacro{in:}%
   \usebibmacro{bybookauthor}%
   \newunit\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{bybookauthor}%
   \newunit\newblock
   \usebibmacro{byeditor:in}%
   \newunit\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {}{}

\xpatchbibdriver{incollection}
  {\usebibmacro{in:}%
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{byeditor:in}%
   \setunit{\labelnamepunct}\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{byeditor}}
  {}{}

\xpatchbibdriver{inproceedings}
  {\usebibmacro{in:}%
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{event+venue+date}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {\usebibmacro{in:}%
   \usebibmacro{byeditor:in}%
   \setunit{\labelnamepunct}\newblock
   \usebibmacro{maintitle+booktitle}%
   \newunit\newblock
   \usebibmacro{event+venue+date}%
   \newunit\newblock
   \usebibmacro{byeditor+others}}
  {}{}



\begin{document}
\nocite{*}
\printbibliography
\end{document}

Guidos way, or - without another package, but with a lot of more code lines - you can change the bibliography-driver for @incollection from standard.bbx, to display the data in your wanted order; change the byeditor+others-macro from biblatex.def to put parencites around the editor data; and change the editorstrg from biblatex.def to use the capitalized version \bibcpstring instead of \bibstring.

\documentclass{article}
\usepackage[style = authoryear-comp, maxnames = 99]{biblatex}

\renewcommand*{\finalnamedelim}{\addspace\&\space} % use '&' before last author in citations and bibliography
\renewcommand*{\intitlepunct}{\space} % remove colon after "In:" for articles in books
\DeclareFieldFormat[article, incollection, unpublished]{pages}{#1} % no word 'pages' for articles in the bibliography (print as is)
\DeclareFieldFormat[article, incollection, unpublished]{title}{#1} % no quotes for article titles (print as is)
\renewcommand{\bibpagespunct}{\ifentrytype{article}{\addcolon}{\addperiod\addspace}} % colon between volume and page ranges for journal articles, period plus space for articles in books

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@incollection{lennon1965,
    AUTHOR = "John Lennon",
    BOOKTITLE = "A book with articles",
    EDITOR = "Paul McCartney and John Lennon and George Harrison and Richard Starkey",
    TITLE = "This is my article in this book",
    YEAR = "1965",
    LOCATION = "Liverpool",
    PAGES = "65--87",
    PUBLISHER = "Cavern Club"}
\end{filecontents}
\addbibresource{\jobname.bib}
\renewbibmacro*{editorstrg}{%from biblatex.def
  \printtext[editortype]{%
    \iffieldundef{editortype}
      {\ifboolexpr{
         test {\ifnumgreater{\value{editor}}{1}}
         or
         test {\ifandothers{editor}}
       }
         {\bibcpstring{editors}}%changed
         {\bibcpstring{editor}}}%changed
      {\ifbibxstring{\thefield{editortype}}
         {\ifboolexpr{
            test {\ifnumgreater{\value{editor}}{1}}
            or
            test {\ifandothers{editor}}
          }
            {\bibcpstring{\thefield{editortype}s}}%changed
            {\bibcpstring{\thefield{editortype}}}}%changed
         {\thefield{editortype}}}}}


\renewbibmacro*{byeditor+others}{%from biblatex.def
  \ifnameundef{editor}
    {}
    {\printnames[byeditor]{editor}%
     \addspace%added
     \mkbibparens{\usebibmacro{editorstrg}}%added
     \clearname{editor}%
     \newunit}%
  \usebibmacro{byeditorx}%
  \usebibmacro{bytranslator+others}}

\DeclareBibliographyDriver{incollection}{%from standard.bbx
  \usebibmacro{bibindex}%
  \usebibmacro{begentry}%
  \usebibmacro{author/translator+others}%
  \setunit{\labelnamepunct}\newblock
  \usebibmacro{title}%
  \newunit
  \printlist{language}%
  \newunit\newblock
  \usebibmacro{byauthor}%
  \newunit\newblock
  \usebibmacro{in:}%changed
  \usebibmacro{byeditor+others}%changed
  \setunit{\addcomma\addspace}\newblock%changed
  \usebibmacro{maintitle+booktitle}%
  \newunit\newblock
  \printfield{edition}%
  \newunit
  \iffieldundef{maintitle}
    {\printfield{volume}%
     \printfield{part}}
    {}%
  \newunit
  \printfield{volumes}%
  \newunit\newblock
  \usebibmacro{series+number}%
  \newunit\newblock
  \printfield{note}%
  \newunit\newblock
  \usebibmacro{publisher+location+date}%
  \newunit\newblock
  \usebibmacro{chapter+pages}%
  \newunit\newblock
  \iftoggle{bbx:isbn}
    {\printfield{isbn}}
    {}%
  \newunit\newblock
  \usebibmacro{doi+eprint+url}%
  \newunit\newblock
  \usebibmacro{addendum+pubstate}%
  \setunit{\bibpagerefpunct}\newblock
  \usebibmacro{pageref}%
  \newunit\newblock
  \iftoggle{bbx:related}
    {\usebibmacro{related:init}%
     \usebibmacro{related}}
    {}%
  \usebibmacro{finentry}}

\begin{document}
\nocite{*}
\printbibliography
\end{document}

Output:

EDIT fixed the issue of multi-volume (with maintitle) and single editor.

A possibility is to abuse the biblatex in: macro to to format and print the information as desired.

\xpatchbibmacro{editorstrg}{\bibstring}{\bibcpstring}{}{}
\xpatchbibmacro{editorstrg}{\bibstring}{\bibcpstring}{}{}

\renewbibmacro*{in:}{
  \ifentrytype{incollection}{%
  \DeclareNameAlias{editor}{first-last}
  \printtext{In}
  \ifnameundef{editor}
    {}
    {\printnames{editor}%
     \addspace 
     \mkbibparens{\usebibmacro{editorstrg}}
     \setunit{\addcomma\addspace}% 
    }%
  \usebibmacro{maintitle+booktitle}
  \clearfield{maintitle}
  \clearfield{booktitle}
  \clearfield{volume}
  \clearfield{part}
  \clearname{editor}
  }
  {}%
}

In this case the "simple" in: contains the directives to print the editors and the book title.

The tricks are: (1) use a guard, \ifentrytype{incollection}, to restrict the modification to the specific entrytype; (2) delete the content of the fields booktitle and editor, thus they are no longer a available in the rest of directive in the driver for incollection, and (3) define a new directive to switch last name and first name for the editors: this can be specifying that editor is an "alias" for the predefined name format first-last, i.e., \DeclareNameAlias{editor}{first-last}.

Notice that the excellent and convenient xpatch package (i.e., include \usepackage{xpatch}) is used to modify how the biblatex string editor(s) is printed. Notice that we need to patch it twice one: the first for the plural version, and the second for the singular case (only one editor).

Here is the outcome: