Two scenarios:
Open arena: hand to hand would be the only way to win. Scott is a better hand to hand combatant every time against Alex. Scott wins.
Inside a Building: Scott has advanced trajectory style aiming. He bounces a few shots around... Knocks loose a piece of building and it falls koing Alex...
Or Alex goes apeshit... Let out a wide out plasma burst... The building collapses... They both get knocked out...
In a best case scenario for ale he manages a tie. In a worst case scenario his older brother beats him up...
Edge: cyclops.