Trying to configure eth0 and eth1 but Failed to bring up eth1

I think you only need one default gateway. You have set up 3: gateway 172.19.20.185, gateway 172.18.182.1 and up route add default gw 172.18.182.1 dev eth1.

Try the following interfaces file:

auto eth0 eth1

iface eth0 inet static
  address 172.19.20.186
  netmask 255.255.255.252

iface eth1 inet static
  address 172.18.182.55
  netmask 255.255.254.0
  gateway 172.18.182.1
  up route add -net 172.19.26.0/23 gw 172.19.20.185 dev eth0
  up route add -net 172.19.24.0/23 gw 172.19.20.185 dev eth0

EDIT: Try this to manually configure the interfaces, so we can see where is the error.

1. Shut down all interfaces: ifconfig eth0 down; ifconfig eth1 down; ifconfig eth2 down; ifconfig eth3 down
2. Configure eth0: ifconfig eth0 172.19.20.186 netmask 255.255.255.252 up
3. Configure eth1: ifconfig eth1 172.18.182.55 netmask 255.255.254.0 up
4. Set up default gateway: route add default gw 172.18.182.1
5. Set up first static route: route add -net 172.19.26.0/23 gw 172.19.20.185 dev eth0
6. Set up second static route: route add -net 172.19.24.0/23 gw 172.19.20.185 dev eth0

Sometimes flushing the interface before bringing it up works:

ip addr flush dev enp2s0