Mounting (getting on top of the other) is a totally normal dominance behaviour - it isnt bullying. It is how the dominant one asserts his authority.
The swaying is called rumble strutting and again is a normal dominance behaviour.
Please do not separate them unless they have an actual fur ball rolling around fight. Separating them unnecessarily will cause stress and can harm their bond if done too much.
Please reunite them. If you leave them apart for too long you have to go through the entire neutral territory bonding process.
The hair shooting up that you report, could be a bit more of a warning sign that things may escalate between them - do read the guides below as they explain more.
It is important you do read the guides linked I've linked in - they explain normal boar behaviours (do check that both your piggies are indeed boys) so you can understand what to expect.
If you seen actual rolling around, fur ball fight and injuries occur, then that means their bond has failed and they do indeed need to be permanently separated if that happens.
Ensure the cage you have for them is big enough - that is 180x60cm for two boars.
Also ensure that you have two of every item in the cage and that all the hides have two doors in them. Dont use any hides which only have one door as it can mean one piggy can get cornered by the other (which can lead to a fight).
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Dominance Behaviours In Guinea Pigs
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