While it does get difficult, in my experience it all comes down to audio.
My current strategy that has beaten night 6 ( with my fair share of luck) is keeping cam on foxy. And checking it maybe every 10 seconds. Then I wait for 5 freddy laughs and whenever she reaches the closest cam I close that side door and completely forget about her until she laughs again. Since chica and bonnie both have audio queues for showing up it's just a matter of checking for when they have left to reopen the doors. As for foxy whenever she isn't in her stage I force her sprint animation by looking st the hall cam and close the door. Ideally you would cam stall foxy a lot more than I do but you don't have time later on ( or the power to do so). Anyways hope this helps and good luck.