when your fish are rubbing up against things and swimming away really fast, it's called flashing, it's usually harmless, but if they start doing it alot, it can be a sign of external parasites.
as for your other questions about their "bonding", there's really no answer to them, they are fish... sometimes they will swim around near each other and sometimes they will all chill in their own part of the tank.
the coloration will also vary from one fish to the next, one fish may have alot of deep red color and others may have hardly any at all, i've seen wild reds that have hardly any color and i've seen tank bred with brilliant red coloration. you can try to increase their color with good tank conditions and a healthy diet, shrimp is a good color enhancer due to their astaxanthin content.
they probably aren't eating as much because they are getting bigger, when they are tiny, they will pretty much eat anytime food is thrown in the tank but as they get bigger, they really only need to eat every few days.