One of my feeders had babies, please help.

[Rhasputin]

As far as determining the mother, the above post is correct. My mice colonies nurse communally, meaning that all of the females nurse all of the babies, not just their own. If your mice are mature, which it sounds like they very well could be, then there is a good chance that it will not matter which mice you take from the cage because the others will pick up the slack.

This is not true. Unless all the females are pregnant and nursing, they will not be able to help nurse the young of another female, and it very much matters who the real mother mouse is. You can find out who the mother is, but either watching, to see who nurses, or lifting the mice one by one, and checking their nipples. The mother mouse will have bare spots around her nipples from the babies nursing.

The best thing to do, is to just leave them all together, until the babies are weaned at 4-5 weeks.

Think of it like getting some free mice. Just keep feeding and watering the mother, and you'll have a fresh batch of mice ready to feed in a few weeks.