You only ever get 1 tag per aspect, so yes, it would be broken, if they both get 1 tag with a total of 2. You can let someone else use the tags you have at your disposal without a stunt, provided the aspect can aid in the action.
The Pack stunt or one putting up maneuvers for the other to use would probably be the best way to go. Or, like Harry and Murphy often do, one is covering while the other one is attacking, so the one that is attacking doesn't have to divert his attention.
Maybe create a stunt as the opposite of "Full Defence", dropping your defence to mediocre for a +2 on your attack roll, while the other takes a stunt, that aids in covering additional people in close combat with a block.