You can keep them together but I find I have better production and survival rate when I separate them before giving birth.
Sometimes Moms play tug of war with babies fighting over them, it can get kinda nasty. Once in a while I get the terrible mom who just kills babies, they become boa food fast and any babies go to other mothers so separating helps control loses there too. Not very often but it does happen.
Many people leave them all together and just consider it part of the process. If you have the availibilty to separate then I would if not you may or may never have problems. Its up to you and what you are ready to deal with.