Humping is a normal part of dominance behaviour for all piggies. As long as the top pig is not stopping the other one from getting food or humping him so much he turns round and bites the other then they will probably work it out for themselves.
If your boys are young then they may well be hitting their more hormonal teenage years where the dominance becomes more important and they start trying their luck with each other. The link given above will give you plenty of advice about what you might spot them doing.
Make sure they have plenty of space - a 120cm cage is the RSPCA minimium requirement for two piggys and more is always better especially for excitable young boars... Make sure they have two of everything so they don't have to fight over food bowls, water bottles, hideys etc and then let them get on with sorting out their pecking order. Just keep an eye out to make sure there is no biting going on.
Good luck!
