I see Gryphon Dynamics suggest a Y6 mixing setup for the 12 motors, but that for DJI motor mixing. As for other flight controller they simply say contact your flight controller’s manufacture lol. We’re flying a X8 with U8pro motors and 28" propellers, but we need a little more lift. With all the issues we’ve seen using U10 motors at higher voltages, a custom HEX 12 seems to be a good option if it’s possible.
It’s definitely not possible with Arducopter, unless you do some creative mixing with motor positioning. ie: set it up as a Hex, but with adjacent motors spinning them same direction, etc.