I'm glad you shared this. I tried to do exactly what you did and leave the pregnant mothers together. I also came up with the same results. I lost some babies that otherwise would have been fine. I noticed as well that one mother would take over all duties and would seemingly be overwhelmed. I had to do quite a few search and rescues and even relocate babies to other moms that were on the verge of weaning their previous litter so that all babies would be taken care of. It made it very difficult to keep track. I am now back to taking out the prego mom and isolating them.