Recently adopted male rats fighting

A couple weeks ago, I adopted four male rats from their old owner who couldn't keep them anymore. Their cage is small for four of them, but there's not much I can do until I get a job. They cuddle each other lots, but at night as they get more active they start fighting a bit and it's mostly just playfighting as far as I can tell (I have two girls in a separate cage that have little arguments, but they've never gotten bad so I'm inexperienced with fighting..) For the first week my boys didn't fight at all, and then I deep cleaned their cage really thoroughly because their past owners clearly didn't know how clean to keep a cage etc, and wiped down their tails that were shades darker than they were supposed to be. Then they started fighting, and it seemed to be getting worse as two of them, Cupid and Iris, had scabs. I don't know how to tell if they're fixed or not, I just know that I'm their third owner.

Are your girls in the same room as them? That could set them off... smelling the girls nearby, specially if they are not neutered. If you found scabs on them, I would also do a mite treatment. Revolution is the best for rats. Also, it can take a month or two for the new guys to settle down and adapt to their new home.

They are in the same room, yes... And I'll try and do a mite treatment soon then. Would the kitten one be best since they're smaller than most cats?

I would suggest treating all of your rats with revolution.
I believe that the difference between kitten and cat revolution is the amount in the tube.
The amount each rat will get on the back of their neck is a very tiny amount/drop, and the amount is based on the weight of each rat and the strength of the revolution.
Many people buy the revolution from their vet and get the vet to apply it.

Here is some info: http://ratguide.com/meds/anti-infectives/selamectin_revolution.php