Hi - I use the unrealBook app on the iPad for music (PDF) display, and it works well. It also has "Master/Slave" setup, where one iPad can control other iPads. I have used this for several years with my band (3 or 4 iPads in use) and it works well. I use a small router that I set to Access Point mode, and I use its 5GHz section rather than 2.4GHz. I find it's alot more reliable than 2.4GHz, mainly because the 5GHz band is just not used nearly as much, so there is alot less "competition" or contention.
It's not absolutely perfect; once in a while we seem to lose synch between the iPads, but very rarely.
Jim