You’re asking some great questions that a lot of people should ask when getting into this situation, because there is some vital information you need to know.

Rabbits do not acknowledge family units, so when they grow up, brothers will not automatically get along, siblings and parents will attack each other to defend territory, etc.. It may be better to forget that they are siblings, just to drive the point home.

Baby rabbits get along not because they are from the same litter, but because they have not developed the body glands that release hormones. The hormones trigger that rabbit to mate and defend its territory. Once a rabbit matures and the hormones begin producing, baby rabbits that got along can suddenly begin fighting and/or mating, over night in some cases.

Every rabbit hits hormones at different times. We’ve had a user have a rabbit display hormonal behavior at 12 weeks old, while my Wick didn’t become hormonal until 8 months old. Because of this variance, the safest approach is keep them separated permanently until they are both fixed, and then waiting a month after each operation to ensure the hormones have time to regulate (there’s a hormone spike after a fix operation, which worsens hormonal behavior for some time).

Separation means separate pens that do not touch, since rabbits can fight and mate through bars.

And yes, sexing young rabbits is notoriously difficult, so be ready for anything!