I'd say just separate any females that you notice fighting together. Generally, female rats will help one another rather than fight, though an occasional fight will pop up from time to time. It's typical of them to "squabble" somewhat though--they have to establish a pecking order in their colony; serious fights like the one you mentioned: definitely separate them. Minor squabbles: let them be.

Did the moms put the smaller pinks back with the other babies? Or have you moved them to an entirely different enclosure? Most of the moms I have will gather all of the babies together in one pile, though if there's a large amount, they'll separate them into two piles themselves. If I have pups and pinks in the same tub, though, I remove the pinks and use surrogate moms from another tub that also has pinks. I've noticed that the larger pups will shove the pinks down to the bottom of the baby pile, and the pinks can't get any milk.

I'd say if the rats really are completely ignoring your smaller pinks, try a surrogate mom if you have one available in another enclosure (just make sure she's had babies fairly recently, and that she still has milk). If that rat refuses to care for them as well, then most likely there is something wrong with them that us humans can't see, but the rats will know and will take matters into their own hands so that the healthy babies have a better chance. No sense in feeding babies who probably aren't going to make it anyway; that's the law of the jungle, and the rats typically stick to it well.