Cat help needed!!!

CeCelia

So we just took in 2 new kitties. A mama kitty and her 4 month old kitten. We have a 5 month kitten and he was NOT a fan of the new family members. That we expected and figured would change in time. But for some reason the mother cat is hissing and growling at her own baby!! What do we do?! Neither of us ever expected something like this to happen. ☹