It can be done - bigger groups of boars (about 10+) can work, provided you have got lots, and I mean LOTS, of space. And the experience/extra space to deal with any troublemakers.
The biggest herd of boars that I have heard of have been about 20 boars, but they had about half a garden with an outbuilding for themselves.
Trios and quartets of boars are particularly unstable; fall outs are pretty much garanteed during stroppy months. With exactly the right character combination, pure adult/adult-youngster bonds can work, but again, it is not something that should be attempted by a newbie because a failure can end up in quite a few expensive trips to the vets, not to mention single boars that refuse to go back together.
Most people I know that have successful trios or quartets have lots of boars and have been able to switch around until they have found exactly the right character constellation of mostly laid back boars. They also have the extra space to deal with fall out problems that happen even to them.