hiysinphlay
What are the dimensions of the cage the two big boys are saying in? How many water bottles, food dishes, and toys do they have? How often and what are they fed? How often is the cage cleaned? All of these factors can contribute to fighting. Typically once they start fighting to the point where they draw blood, it only escalates from there unless action is taken.
I have one boy right now that is being separated from his cage mates because he just won't stop fighting with them .-. I've done everything I can think of. They are 3 rats in a cage large enough for 6 TONs of toys, 5 water bottles, multiple places for food. But he still fights with them, and has left scars on both the other boys.
The cage is 79.5 x 50 x 80cm, it's the Jenny cage by Furplast (apparently you can keep 4 rats in it easily). They have several toys and are regularly given new boxes to hide and play in, as well as all the boxes and paper bags they get outside their cage. They have one dish (a big one) and one water bottle on two different levels of the cage. They're fed kibbles, also called rat nuggets that're meant to be nutritionally complete and have recently come off muelisi. The cage is cleaned daily, thoroughly cleaned once a week.
Sorry to hear about your boy living alone, I'm starting to think that might be the only way for mine. He's so nice with human beings, but just a pain in the neck to other rats.