Dominance Fighting?

[Emily Beth]

The other day I noticed my boys were being rather aggressive towards each other. The less dominant one since I have had them was jumping on the dominants one back and seemed to be doing something that looked like humping. After this it got worst and the dominant one was throwing the other off his back and they both started what seemed like they were chatting they teeth to each other and seemed to face off. They would then go and chase each other biting and throwing each other in the air as they went. I don't know what to do and I wondered why they were only just starting to fight after having them for 2 years. Should I leave them to it, separate them or try something to stop it.