I’m so sorry <3 I had kittens with terrible diarrhea and lost two and nearly lost several more. What seemed to help them was kitty-dt (digestive support drops I got from a local pet store, but Amazon has it too) and metronidazole prescribed by the shelter. You could also try an anti diarrhea medicine - Petco has some you might be able to go get right away. I really hope they pull through and thank you for fostering 💛