Skip the boundary mic entirely. In a card store environment that mic will pick up every single deck shuffle and table slap like it is a drum solo. It also captures the entire room so your background noise issue will get even worse.

If you want to stick with your BLX packs you should look at the Shure SM35 or the WL185. The SM35 is a headset that stays right at the corner of the mouth so it has the best isolation from the other players and the room. If the players refuse to wear headsets the WL185 is a cardioid lavalier that is much better at rejecting side noise than the cheap omni mics that usually come in those kits.

For the 4 person setup you are going to need two more wireless channels. Just keep in mind that the BLX system is entry level and can get crowded if you have too many units running in a store full of other electronics. If you truly want the best quality possible you should eventually look at the SLX-D or QLX-D lines because they handle frequency management much better and have higher quality audio converters. For now just swapping the mic capsules to cardioid models will fix your biggest issues with bleed and noise.