Alright, fair enough. I guess I should have said that I wouldn't be brave enough to take off that much time during API academics. I took off a day the weekend before Aero 2 because my dad was in town, and my score suffered. I wouldn't want to give up an entire weekend plus all the time before that's required to fulfill the duties of being a best man.
My main point was that this guy cannot say for certain when he's even going to OCS, how long he will be there, or how long he'll spend in A-pool, thus what part of training he will be in at the time of the wedding. And I know I can't say anything about what his chances are of taking leave during Primary, haven't gotten that far yet.
If the timing is right, you'll have no problem being your brother's best man. If it's not, you may have to make some compromises.