My baby ratty girls are having babies. Any advice?

Ok, so I put my two girls (roughly 6mth old) in with my boy Basil (2.5yr) a little while ago. Now they're pregnant. I had hopes that they'd get pregnant.. but was convinced until a week ago that they hadn't even mated. Basil just didn't seem interested in them like that and I was always checking for a mucus plug or signs they'd done it.. but didn't see anything. Now the girls waist lines are expending and their are becoming more noticeable. I weighed them last night and again this morning and both girls have gained about 4g since last night. I'm going to continue weighing them and seperate them from Basil either tonight or tomorrow (Poor boy is going to be so sad).. but I'd really like some advice from someone with experience. Should I seperate the girls before they give birth, how long before? How long till they can be put in together again? The girls have been together all their lives, and I think the smallest one would freak out without her sister, but I don't want them fighting over the babies. Any help would be greatly appreciated.