I have 3 airport express routers, one at FOH, one at monitors, and one as a master. They all share the same network (the router at each console extends the master network).
I've had as many as 11 musicians simultaneously on iPad/iPhone, plus me with my iPad. I noticed a couple hiccups on my iPad, running x32 mix, over the course of a 3 day show, but the musicians didn't notice anything. I think I only noticed those small hiccups when I was connecting to the monitor console, not FOH. I know Behringer doesn't recommend connecting more than 10 devices, but you should definitely be good with 5 or 6, especially if I can do 12.
Maybe the fact that I have multiple routers helps, maybe it splits up the load or something, I don't know. I've also never run x32 edit in a live situation, so maybe that has something to do with it too.