As others have said, keep an eye on them but don't worry too much. Having them indoors is good because it means you are much more likely to spot any signs of trouble.
As they grow up, boars will go through certain behaviour rituals to establish which one is going to be 'Boss'. Normal boarish behaviour includes 'rumblestrutting' which is exactly what it says and unmistakeable once you've seen it. ;D...the boar sways his body from side to side whilst either walking up and down or moving from one foot to another on the spot, and makes a 'burring' sound. Boars may also sniff each other's bums, attempt to mount each other, and do nose-to-nose face-offs. There may also be a little bit of teeth chattering. All of this is within the range of normal brotherly squabbling/dominance behaviour and just what boars do. O0
What you need to watch out for is: sustained/prolonged loud teeth chattering, possibly accompanied by ruffled-up fur, raised hackles and 'yawning' (displaying teeth) - which are the signs of an impending fight, which can happen if neither is prepared to back down and accept the other as boss. Even at this stage, though, they may back off without a real fight taking place. Don't separate unless there is a real serious fight.
Or, alternatively, if one bullies the other...look for bitten ears, or if one boar seems to be scared of the other, not eating, or huddling in his pigloo.
Most boar partnerships go through the dominance thing, and most reach an understanding without needing any interference from humans. As I say, by keeping them indoors you are doing the best thing as you can keep an eye on them without affecting their natural behaviour.
