I’m sorry to hear the falling out has happened already. Unfortunately there was always this risk in taking on three teenage boars.
As I think I mentioned on your other threads, moving to a new environment causes them to reestablish their relationship. In tense and unstable bonds (and a boar trio is one of the most unstable) the move can cause a breakdown in the relationship. In two compatible piggies and a bond which is functioning they will still reestablish. It will see a bit of extra dominance behaviour but it should settle after around two weeks.
Your boys now need to reesstablish but also establish as a new hierarchy as a pair.
Rumblestrutting is a normal dominance behaviour and, on its own, is not a reason to separate. However, you need to take their behaviour as a whole to gauge their relationship. They will need to come to an agreement between them over which one is the dominant and the other has to be prepared to back down. If he does and they are compatible then they will likely be ok as a pair. If he doesn’t, then their pairing will also fail and they too will need to be separated.
The first guide below explains the levels of dominance and the behaviours you might see at those levels.
The second guide explains how to spot a dysfunctional bond and how to test it. The temporary separation for a few days and neutral territory reintroduction is a one time thing - it allows them to make their own decision as to whether they actually want to be together. You should not repeatedly separate and reintroduce boars.
The third guide explains teen boars in more detail.
Do give them all a read as they explain everything more fully than we can repeat in every post
Dominance Behaviours In Guinea Pigs
Bonds In Trouble
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?