You do whatever you feel is right for Bobbie. My gut feeling would be to leave the new babies in with her and make a play area for the older babies and supplement them with milk if needed. I believe the first priority is Bobbie and her existing babies and maybe the new ones will make it. If she was still with the breeder then he'd certainly wouldn't handrear any and he must get litter after litter from these poor does otherwise he wouldn't remate them so soon, so you may find she'll cope, somehow However you're the one in this awful situation and I do feel for you. Keep calm and a straight head if you can and think things through before making a decision in a panic.
Good luck with them, Kathryn x
Good luck with them, Kathryn x