I usually have 2-3 females in tub together with babies too. They all help feeding the babies.
I had 3 together, 1 wad still nursing the babies, even tho her babies were 5-1/2 weeks old. I just removed her yesterday as some of the varies (19 of them) are starting to get weened and I figured 2 moms can handle them.
I do have 3 females in with them too (8-1/2 weeks old).... they are not nursing the babies, but I believe that they are "learning" to be good moms. Plus I think they are learning that my hand touching the babies is okay (for when they do have their own babies).