Pregnant Jack Russell?

Hi..I recently took on two Jack Russell dogs from a local rescue centre. One is pregnant (from before she went to the rescue centre). I was warned that because both are female there was this possibilty but they couldn't be sure whether they were or weren't(they were dumped at another kennel and they think possibly they had been used for breeding , are about 2 - 2 1/2 estimated guess by vet). I took them to be checked out by the vet at the weekend and she confirmed Molly is pregnant and due anytime in the next two weeks. The rescue centre has offered to help find good homes for the pups. I have no idea how many she is likely to have, what breed the father is! I have read up on the internet about the birth etc but any advice would be appreciated. Also as a seperate issue, I have noticed Molly(the pregnant one) is very domineering towards Maisie and often sits on her growling. I understand that dogs have a hierarchy but have I done the right thing taking on two females (thinking they would be better in the same home)...is there a way of dealing with this sort of behaviour without making it worse as i and the rest of the family love them both to bits and would like to keep them on but don't want Maisie's life being a misery? any advice greatly appreciated. Thanks.