cats

Unfortunately there's probably no way to know for sure, outside of DNA tests or something like that, whether that's the mom or not. From the outside it's hard to tell. Cats don't have human-like family relationships to each other. Sure, the moms usually care for the kittens but they also do that for kittens which aren't their own. They also likely won't recognize their own kittens anymore (and vice versa) after some time has passed and their smell has changed. They probably still care for them out of instinct or social habits but not necessarily because they know it's their child. From their behavior it might look like they know but they might just as well not.