To the OP. Kick the WAAC players out. Seriously. Its your store, you set the tone and if people are ignoring you tell them to play somewhere else. If you feel nice give them a single warning. Something along the lines of "Start playing nice or go somewhere else". When you have WAAC players that refuse to adjust behavior it actually makes you lose sales you would otherwise get from players who don't show up. That is not sustainable.
Once you've gotten them out then set up a weekly play night that has prizes. Make up some sweet objectives numbered one through six and give one out each night to players that get two league games in (Maelstrom of War missions only). Each game you win gets you a ticket into a drawing at the end of the league. Then, at the end of the league have a drawing for a store credit.
The point is to get people playing regularly again, hopefully forming a habit.
I cannot emphasize enough that it is your store and YOU get to set the tone. If you don't you are not providing the best service to your customers and they will abandon you.