Definitely have a word with your brother. Maybe he doesn't understand how hurt you are.
For the rehearsal party, you are supposed to be invited. "All attendants, the bride and her fiancé's immediate families, the officiate and spouse, as well as any out-of-town guests are included in the guest list" according to
this site . You are immediate family.
As for being in the wedding, it's up to the couple whom they ask, but it does seem a little odd they'd ask her siblings and not ask you. If she doesn't want you as a bridesmaid, there's no reason your brother can't ask you to be one of his attendants. If it looks weird to have a female "groomsman" or if it unbalances the numbers of attendants on each side, so what? Or you could be asked to do one of the readings or something. It's up to them what they ask you to do, but as the groom's sister, you should have a special role in their ceremony.