There are a few people dotted around who have stable quartets and trios. Many of those have quite a few boars and plenty of space to switch around until they have found the right mix.
I understand that it gets easier again if you have a real herd of boars. I have come across of somebody in Germany who has a herd of 20 boars, who live in a huge run in part of her (large) garden with a whole outbuilding to themselves.
Bonding bigger groups CAN be done, but it hinges very much on experience and the right combination of characters - and LOTS of space. There is also usually a mix of ages involved rather than a same age group; and you can't have more than one dominant boar per group.
However, unless you know boars very well, you are more likely to end up with murder and mayhem, so it is NOT something to be tried without a lot of forward planning and the possibility of accommodating every boar singly AND make him happy if things go really haywire!