Each betta is different and has different moods/emotions when it comes to company. You can test it out, but I would put atleast 3-4 and no less toghether that way if they are aggresive, it can be divided amongst them instead of just on one. Some may do great, others will just kill and terrorize, so watch out. You could put them in a divided tank without a problem though. If you use 2 males, just watch them for any added stress they might show. Some mind it, but I think most do fine next to one another.