Is it possible to connect two or more bluetooth controllers to one android tablet? I am wanting to emulate some games that are four players and I want to know if three friends and I can all play together?
This is a bit of an opinionated, and caveated answer.
According to the Android Developers you can indeed
"Manage multiple connections"
It seems to be the case than an Android tablet can connect with multiple Bluetooth devices sending data only, but Bluetooth devices that can also receive data will only pair with one device.
From my trying this on:
Galaxy S5 (phone not tablet obviously)
It only allows one controller and disconnects the others. We had some patchy performance with two working, but Bluetooth is not a good technology for multiple connections like this.
You certainly can contact up too 4 controllers simultaneously but the way I achieved this was with a rooted note 4 just install sixaxis and there is support for multi play... I hdmi into tv and vs my mates with ps3 controllers (work best, even non genuin) also if you are using emulators n64 emulators have multi support inbuilt but you still need sixaxis to connect through Bluetooth.
It's perfectly possible with at least Android 6.1 and above to connect up to 4 bluetooth controllers.
Just pair the first controller, turn it off, pair the second controller - and turn the first on again.