Hi there. I just did something similar, I have a geared hub motor front and back, two controllers that are compatible, and one battery. For the display, I just have it read from one of the controllers. I currently have the throttle wires in parallel going to both controllers, which works great, I just did a snow trail ride here in Alaska and the AWD was awesome, compared to the previous rear wheel only, especially on steep hills or punchy snow. Anyway, the problem comes in with the PAS. I currently have the PAS going to both controllers, but the display can only accept speed input from one. If I tie both communication wires of the display (that give speed input) together for both controllers, I get an error. So, with only input from one controller then the other controller thinks speed is always zero, so it wants to go full bore, no matter what PAS level is selected. Perhaps someone with more knowledge on this could chime in, but seems like with two potential speeds from the two wheels (slipping on snow, mud) the display would always be confused with the duplicate input. So.... I will probably change this to PAS on rear wheel only, and let the throttle be for both wheels, so if I need the front wheel for tough terrain, I will use the throttle, which seems to work fine in a parallel wiring configuration. Your results may be different with a different controller/display combination, but this is my experience.
Another thing for your particular case with such large hub motors, you will want to make sure your battery, BMS, and all associated wiring can handle another 40A. I just have a 250W in the front, and just that little bit seems to be enough to keep the front wheel from being a liability in the soft stuff
Cheers,