By law in Brazil, people who are over a certain age, or disabled, or families with young children, etc, are boarded first and there is a designated priority lane for this group. Not entirely certain if the priority that comes with the exit row seat allows you to use this lane. Also, by emergency seat, I presume you are referring to the emergency row? If so, do you speak Portugese, otherwise they may re-seat you. You can also get extra legroom by purchasing Comforto seats, usually the first 5 rows. I don't think the carry-on and backpack will be a problem.