He refuses for me to walk down the aisle to anything else. What do I do to get him to agree with my music

My boyfriend and I are traveling 5 hours for his sister's wedding next month. We'll both be attending the rehearsal at 4pm the night before the wedding followed by the rehearsal dinner at 6pm, which is at a separate location from the rehearsal itself. What exactly is a rehearsal? My boyfriend is a groomsmen and the brother of the bride so will he be sitting at a separate table during the rehearsal or dinner, or will we get to sit together? Also what should I wear to the rehearsal? The wedding is "cocktail casual" but does this apply to the rehearsal as well? Would a sleeveless chambray dress with a belt around the waist be appropriate or is that too casual? Sorry for all the questions but thanks for taking the time to answer! :)