Biplex: an important useless operator

Pyth, 26 25 bytes

JsM.T_MjR2Qi_}RhM_BS-J0J2

Try it online: Demonstration or Test Suite

Explanation

JsM.T_MjR2Q
       jR2Q      convert each input number to binary (lists of 1s and 0s)
     _M          reverse each list
   .T            transpose (with top justify)
 sM              sum up each list (numbers of 1s at each position)
J                store this list in J

i_}RhM_BS-J0J2
         -J0     J without 0s
        S        sorted
      _B         create the list [sorted, reverse(sorted)]
    hM           take the first elments of each (bitsum-min and bitsum-max)
  }R        J    check for each value in J, if it is part of ^
 _               reverse this list of booleans
i            2   convert from binary to base 10 and print

Minkolang 0.10, 109 79 bytes

(n1$(d2%$r2:d)99*I-DmI2:[+1R]$I)rI$d$(s0(x0gd,)Ik3R2g1-X0I3-[2*2gd0c=$r1c=++]N.

Input and output are in decimal. Try it here.

Explanation

(                            $I)    Loop until input is empty
 n                                  Read in number from input
  1$(       d)                      Start a while loop with only the top of stack
     d2%                            Next least-significant bit (modulo by 2)
        $r                          Swap top two values
          2:                        Divide by 2
              99*I-D                Pad with 0s
                                    (when the while loop exits, top of stack is 0)
                    m               Merge (interleave) stack
                     I2:[   ]       For each pair...
                         +1R        Add and rotate stack to the right
                                    <<This does the work of computing bitsums>>

r       Reverse stack
 I      Push length of stack
  $d    Duplicate whole stack
        <<This lets me sort the bitsums without affecting the original order>>

$(                      Start while loop with <top of stack> elements
  s                     Sort
   0(     )             Push a 0 and start another while loop
     x                  Dump top of stack
      0g                Get front of stack and put it on top
        d,              Duplicate and <not> for end-while condition check
           Ik           Push length of stack and break out of while loop
             3R         Rotate [min, max, length] to front
               2g1-     Get length and put it on top, then subtract 1
                   X    Dump that many elements off the top of stack
                        <<Now I have min and max>>

0                        Initialize decimal with 0    
 I3-[               ]    For as many bits as there are...
     2*                  Multiply by 2
       2gd               Get the next most significant bit and put it on top
          0c=            Copy min and check for equality
             $r          Swap top two elements of stack
               1c=       Copy max and check for equality
                  ++     Add 1 if bitsum item is equal to min or max, 0 otherwise
N.                       Output as integer and stop

Old version:

$nI[(d2%i1+0a+i1+0A00ai`4&i00A2:d)x]00a1+[i1+0a]s0(x0gd,)rI2-[x]00a1+[i1+0ad0c=$r1c=+]0gx0gx0(xd,)0I1-[2*+]N.

Try it here!

Explanation

The crux of it is that the array feature is heavily used (a A) to store the bitsums, of which the minimum and maximum are found, then 1s and 0s are outputted appropriately, with dumping of leading 0s in two places.

$n                                      Read in whole input as integers
  I[(                             x]    Convert each number to binary
     d2%                                Get next least significant bit (modulo by 2)
        i1+0a                           Get current value in array for that position
             +                          Add
              i1+0A                     Put current value in array for that position
                   00ai`                Get first value of array (bitsum length)
                      i`                Greater than loop counter?
                        4&i00A          If not, put loop counter there
                              2:        Divide by 2
                                d)      If 0, exit loop

00a                Get first value of array (maximum length
   1+              Add one
     [i1+0a]       Get bitsum values from array and push on stack
            s      Sort
0(                 Push a 0 (for dump) and start a while loop -- dumps leading 0s
  x                Dump top of stack
   0g              Get bottom of stack
     d,            Duplicate and <not> it
       )           Exit loop when top of stack is non-zero (i.e., the minimum)
        r          Reverse stack (so now it's [min, max, <stuff>])
         I2-[x]    Dump everything else

00a1+[               ]    Get bitsum length and loop that many times
      i1+0a               Get bitsum value at current position
           d              Duplicate
            0c=           Copy front of stack and check for equality
               $r         Swap
                 1c=      Copy next-to-front of stack and check for equality
                    +     Add (so it's 1 if it's equal to min or max, 0 otherwise)

0gx0gx       Dump front two elements of stack (the min and max)
0(xd,)       Dump leading 0s
0            Push 0 for conversion to decimal
 I1-[   ]    For each bit...
     2*+     Multiply by 2 and add
N.           Output as integer and stop

J, 31 30 24 23 21 bytes

+/(e.>./,<./@#~@)&.#:

This is a tacit, monadic verb that takes a list of decimal integers and returns their decimal biplex.

Thanks to @Zgarb for his suggestions, which saved 4 bytes directly and paved the way for 2 more!

Thanks to @randomra for golfing off 2 more bytes!

Test cases

   biplex =: +/(e.>./,<./@#~@)&.#:

   biplex ,1
1
   biplex ,2
2
   biplex 1 2 5
7
   biplex ,4294967295
4294967295
   biplex 2454267026 2863311530 3681400539
3817748707
   biplex 2341103945 2969112506 1849078949 1430639189
3

How it works

                 &.    Dual. Apply the verb to the right, the verb to the left,
                       and finally the inverse of the verb to the right.
                   #:  Convert the input list from integer to base 2.
  (            @)      Define an adverb, i.e., an operator that takes a verb as
                       its left argument.
+/                     Call it with "reduce by sum". This calculates the sum of
                       the corresponding binary digits of all integers before
                       executing the remainder of the adverb's body, i.e, this:
             #~          Replicate the sum N a total of N times, i.e., turn
                         0 1 2 3 into 1 2 2 3 3 3. This eliminates zeroes.
         <./@            Calculate the minimum of the result.
     >./                 Calculate the maximum of the sums.
        ,                Append; wrap both extrema into a list.
   e.                    Check if each of the sums is in the list of extrema.
                         This yields 1 if yes and 0 if no.
                       (from &.) Convert from base 2 to integer.