For the ones who lost toes, I went through the same thing with a rescue. What you have to be careful of here is that if the feet are infected, you will need antibiotics to make sure the infection doesn't get in the bones of the leg.
My girl had hard crusty junk all over the feet with only one toe left on each.
The routine was soak feet, goop on lots of plain Neosporin, non stick pad on bottom of foot, wrap lightly with gauze, tape. Every other day. Trim the nails little bit by bit like mentioned above.
The pad on the bottom of the foot made walking less painful, the Neosporin sofened the crust and after a bit, came off so you could see better what was left & needed to heal. Wrapping kept dirt out as well.
I realize you have a lot of birds here, so this may only be practical for the worst cases and with a friend or two to help.........
Kudos to you for taking this on! Keep us updated.
ps, forgot to add, when they heal, there may be nerve damage, in winter they may not be able to keep the feet warm enough and will be susceptible to frost bite.....