with "Barbaric" can i uncommit 4 cards at ones if i had 4 "Barbaric" and then use the uncommited cards ability again?

Yes. After your attack deals damage you may ready any 4 foundations of your choosing (including your opponents). Then on your next attack, you may use those readied foundations (if you control them) to enhance/form/respond again.

Hayamachop is correct that you may play them, but once one Barbaric resolves the others are not able to. They do not resolve simultaneously. Playing multiple (non-cancelled) Barbaric's would only benefit you in the case of trying to play something else such as, for example, trying to play Dirty Pool's enhance.

oh doh. Forgot about the cannot ready anymore foundations this combat phase.