I leave the males in with the moms, harem style. I don't have issues.

Occasionally a rat will kill and/or eat babies. It could be the mom or dad. Disturbing the babies can make a new mom freak out and kill them too, so if it's her first litter, I would not mess around at least a couple days.

Just feed and water mom/dad well, and make sure the cage is clean. That's really all you need to do. Rats have taken care of their babies since time began, so they're pretty self-sufficient in that regard. If mom starts to look thin from nursing a lot of babies, you can give her supplements but otherwise, just regular food and constant clean water.