Do you mean tower 1 2 and 3 are the levels of upgrade or are tower 1 2 and 3 different types of towers? You shouldn't have a problem with this because if you say tower 1 touched - change variable, it should only affect the tower being touched, not pick all of them.
Edit: Ok I see your screenshot now, it would make it easier if you did 'on object tapped', the hold gesture will pick all towers.