Two female rabbits may or may not get along if introduced as older juniors or adults. It really just depends on the individuals. If introduced when they are young they should be fine.
Two male rabbits, however, will almost certainly fight as they mature, even if they brothers housed together from birth. Two males that are introduced to each other as older juniors or adults will almost certainly fight and may injure each other badly.
An un-neutered male will probably try to breed and then to fight any other rabbit it is housed with. However, the following combinations will probably get along okay.
-Fixed female and un-neutered female
-Fixed male and un-neutered female
-Two fixed rabbits.
Also, pet rabbits that get a lot of human attention usually are happy enough without another bunny. Though most rabbits enjoy bunny company, not all of them do and it's not required for happiness. Also, keeping two rabbits in seperate cages with a wire divider between them allows socializing without such a risk of fighting.