Chell, if it were me, I would want to take them to the vet and get them checked over. What I would try in the meantime, if you think the weaning too early was the problem, would be to mix their wet food with kitten milk replacement formula or canned goat milk (you can get it in the baking aisle at Walmart, I’m told), warm it gently and see if they have more success with that. Even if they’re only four weeks, they should be able to eat wet food mixed with KMR or goats’ milk (don’t give them cows’ milk, they can’t digest it).
You did the best possible thing by putting them back together. Is there any way your mum’s kitten and yours can live together for a few more weeks? That would stop them being lonely and the one who’s doing fine will be able to help teach your one about pooing and eating etc (as long as there’s no medical problem involved with your one). I would want to keep them together until you think they’re both about at least eight weeks and probably 12 weeks would be better. Cats learn from each other 🙂
