Hi and welcome!
Three boars have unfortunately a very high rate of failure, about 90% once they hit the teenage months or when you introduce a third, even more so in sub-adult boars.
You either end up with one dominant boy waging war on the other two, the two more dominant boys going to war between them or two ganging up on the weakest. That brothers don't fall out is sadly a persistent but long debunked breeder myth.
Please take the time to read our teenage guide here. Ideally you split the problem boy from the couple that is getting on and keep him as as next door piggy with round the clock interaction through the bars while you consider your long term options, which you can also find listed in the link:
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?