Putting three boars together rarely ends well.
You can of course try it if you wish but do prepare that it is likely to fail. Not only that it can also bring about the downfall and ruin the bond of the original pair as well (meaning you are left with three single piggies).
Generally speaking, we would advise you to not attempt a trio and instead keep the pair in one cage, and keep the single permanently alongside in a separate cage.
For you to attempt a trio, the c&c would need to cover at least three square metres (so approximately be a 9x3 c&c cage), and any attempt at bonding must be done on neutral territory, with the preparation to split the cage back up.
Very occasionally somebody will get lucky with a boar trio, and you never know you may end up being one of them, but it’s best to prepare for it not to work. Sorry we cant give better news on that front
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?