My 2 brothers are walking my mom down the aisle at my wedding...Are they called ushers or groomsmen?

If the brothers are only escorting guests to their seats then they are ushers, and they usually sit in the front row, or can stand next to the groomsmen. If they stand next to the groomsmen they walk out last after you, and the bridesmaids and groomsmen. If they sit next to your parents, then they would walk out with them after the wedding party. Also they generally wear a tux, or they can wear matching suits, and they should have a boutonniere also. Hope this helps and congrats on the wedding.