They are right in the middle of their teenage months (4-14 months of age) which is the most difficult time and a real test of two boars bond. Character compatibility is the key to a successful relationship between two piggies. Normally the relationship between two piggies who have been correctly matched and like each other will get through their teens with just mild dominance and come out the other side intact. However, you specifically mention bought, which leads me to think pet shop bought rather than rescued. Sadly pet shop piggies are not often correctly character matched when they are sold so these kinds of problems can sometimes occur when they get to their teens and decide they don’t like each other.
The mounting and little well placed nips are not of concern in themselves - it’s dominance, but if there have been injuries caused, then things may be more serious than just dominance.
Giving them some time apart to calm down is wise. You can attempt a neutral territory reintroduction and see how they get on. If they fight, then they won’t been able to live together again. If they must live separately going forwards, then you need to ensure each of their cages is big enough (a minimum of 120cm x 60cm each) and that they are next to each other so they can still interact through the bars to prevent any loneliness occurring.
Lack of space can be a real issue between teenage boars. Most pet shop cages aren’t big enough which can exacerbate issues. Two Male piggies requires a 180cm/6ft cage with multiple hideys, bottles, food bowls etc to help reduce their reasons to bicker. However, if two piggies don’t like each other, no amount of space will heal a rift.
I will add in some guides below which give further information. It is important you understand the differences between normal dominance/teenage behaviour and actual breakdowns in a relationship
Bonds In Trouble
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Dominance Behaviours In Guinea Pigs