It is possible to use more than one tablet or phone at the same time by running more than one instance of the Knobbler device. Each instance is fully independent — its own port, its own mappings, and (see below) its own current track and device — so several surfaces can drive a single Live Set simultaneously.

Above: two iPads — one on the mixer, one on a device page — plus a Push, all controlling the same Live Set at the same time.
By default every Knobbler surface follows Live's selected track and device, so they all show the same thing and stay in sync with what's selected on screen. That's ideal for a single player.
For multiple surfaces at once, each instance can instead hold its own current track and device, independent of Live's selection and of the other surfaces. Tap the Follow Sel button in the toolbar to toggle:
So one player can ride the mixer while another tweaks a synth's macros and a third drives an effect rack — each on their own tablet, none stepping on the others' selection. The lock state and the chosen track/device persist with the Live Set per instance, so each surface comes back where you left it.
Requires a Knobbler device and app version that support the focus feature (the Follow Sel button appears in the toolbar when both are recent enough).
Each instance exposes a Live parameter named Device Port, so you can give each one a unique port from anywhere you can change Live parameters — even on Push 3 Standalone.

Device Port number to 2345.2345. If one does not appear, then just enter the port number manually above.2346).2346. If one does not appear, then just enter the port number manually above.