If you put a boar with sows, he obviously needs to be neutered (with a six week wait after his operation), or you will be ear deep in pregnancies!
As to getting brothers - you have as much chance of them making it through puberty as with a unrelated boars; it's the constellation of characters that counts more than anything else - whether there is an age difference, so they won't hit puberty at the same time, or whether they have grown up together from birth! We have had several fall-outs from siblings in the time I have been on this forum, so that is no guarantee.
I still would strongly recommend to get an already bonded pair from a rescue - that way you can be sure that they ARE getting on! Rescue people usually take great care with the bonding, as they have every interest in rehoming a stable pair.