I personally would try the safety gate as well so they cant get out. I would leave them in there.. together.. even if they fall asleep on the floor while playing you can go in and put them into there beds later..
Since they think its a game you going in there every 2 seconds.. not going in at all.. they wont get the same excitment as before.

Even if they need to poop.. I have left my son in his room till the morning, and then he went in the morning.

Good luck.. such a nigthmare!