We have the same problem with our little Gabby. He's the one with Feline Aids (FIV). The vet has him on a dry food called Premium Edge (www.premiumedgepetfood.com). His stools are normally soft but solid, but sometimes very liquid. Either way he's gained back a bit of weight, the patches of fur that fell out are growing back in and my boy RUNS again. Purrs like a diesel truck too.

Don't disregard the throwing up as a "sensitive palate", get things checked now. We almost lost our Gab.

If you do find a food that works for them, you need to feed them separate and keep them out of the other's chow. It's hard, but it's like having a "special needs" child.