Their root systems will entangle and compete. Once the roots are entangled, which happens quickly, it is difficult to separate the plants without damaging the roots. If they are left together, one plant may become dominant, but both plants will likely suffer. It's not a good idea, but I have seen two plants flowered together in the same container.
it is possible to do this i have seen three in one pot with a far below average yield. so if you must do it this way then you can. but you should really get two separate pots your yield will increase dramatically.