Space is a big factor in boars bonds. The more space the better as it reduces bickering and gives them space to be alone if they want. Having two of everything also reduces bickering over food bowls etc. They will always have a little to and fro as it's important that they maintain their dominance hierarchy so one of them will always be top pig!
Buddy baths like
@Gia mentions can work but are a last ditch thing in my opinion as removing their smell by bathing can sometimes have the reverse effect and lead to more arguing as they re-establish their dominance. Mainly they work because they unite piggies against the common enemy - you for putting them in water... And once the stress of a bath wears off (and baths do stress most piggies out a bit as they aren't natural water lovers) then the problems can return but as Gia says, it worked for her guys and it has it's place.
They sound like they do get on in general and
@Wiebke has given you some great links to information so hopefully you can keep your boys happy. They sound just like they are working each other out but doesn't sound like anything to worry about.