I think the only reason people are finding your question a bit odd is that it seems like a risky thing to do. In general two males with one or more females is sooner or later going to result in fighting. Piggie naturally live in herds headed by one male and his group of females and pups.
Just because your boys don't show any interest doesn't make them odd, just happy in their own company which is fine.
I wouldn't suggest repeating the experiment though because it is very likely you could destroy the friendship of the two boars by challenging their bond and end up with two single, unhappy piggies which isn't great for anyone. It's not just as simple as making sure they are not able to have babies although that is also very important!
