The general rule with rats is "no blood no foul", if they aren't hissing and siddling up to eachother and actually drawing blood chances are they are playing and establishing dominance. Rats are quite the drama queens so it isn't unusual for lots of squeaking and rough housing to be present during play.
That's just how boys are. 8) Anyway it's like what Darksong17 said "no blood no foul". I've noticed most rats fight play or dominance and my guess is becuase they are brothers it's play. Just like people.lol