Based on my experience, there is a problem with 2 players. The game would only let me and my brother play (both using different profiles on the Xbox One) an Exhibition game. When we tried to play 2 player in MY GM MODE, it would only recognize one controller. If we backed out, it would recognize 2 controllers, if we chose exhibition.
Unfortunately, for some reason they removed 2-player support from MyGM in a day-one patch.