Mounting and teeth chattering are entirely normal dominance behaviours between boars and not, on their own, a sign of a problem. You haven’t said how old they are, but seeing an increase in dominance when they (or one
Of them if they are different ages) hit their teens is entirely normal. It’s only if they aren’t compatible and they can’t come to an agreement over who is dominant , or if the younger one makes a play to be top pig and the dominant doesn’t like it, that you need to separate them but otherwise you will see dominance behaviours from boars throughout their entire lives - my two year old boar pair love nothing more than mounting and rumbling at each other. As this is a health thread though , if you would like a discussion further advice about this, then do open a thread in the behaviour section
Regarding the nose, only a vet is going to be able to tell you if there is a medical issue going on there or whether it is caused simply by him putting his nose through the bars