I wouldn't guess that you have any medical records on this kitty?
I would IMMEDIATELY have them combo tested for FeLV/FIV. It is critical.

Then, I would worm them, as if they have worms. It is cheaper to treat them, than to test them (fecal)

If you can, bathe them in a fungal shampoo, in case of Ringworm too.
Look for fleas or bite wounds.

In the foster room, make sure there is a 'safe spot' such as a hidey hole, a covered tupperware with a hole in it, or the carrier.

They are going to be alright, and thanks for helping.