One of the reasons, they are probably fighting with her because of the baby. They probably see Abbi as a threat and want to protect the baby. Also, many females that are already bonded with a male will never accept another female. This is why when breeders want to make a trio, they suggest you have 2 bonded females and introduce them to a male. So, your older female probably doesn't want Abbi around.
The best thing for you to do right now is to keep Abbi separate from everyone. First off, she is only 4 months old and you do not want to take the risk of her accidently getting pregnant since it can be very dangerous for her while she's so young. Later, when your other chins don't have a baby, Abbi is older, and it's safe for Abbi to breed (assuming she and your boy have pedigrees) then you could try seeing if you can slowly introduce everyone properly and have playtime together.