My friend and I have raised rats for both food and pets, I have kept everybody together, a lot of time we don't even take the father out unless the moms need a break. About the only time I separate the mom is if the cage I have them in won't work for babies, some of my pets are in chinchilla cages that babies can escape from. If the moms do fight over the babies I would separate but other than that leaving them together should be fine, I only really had a problem once but the other mom had lost her own litter. Every rat is different so once you know how they act,you will know how to proceed in the future.