Sinice he can scale a baby gate, how about putting one baby gate on top of another in the doorway? They should stay that way when they are "locked" into the doorway.
I doubt that this is sleep walking, with all the things he is getting into and waking his sisters up.
If you have an old house with winged doors, then have a piece of plywood cut the width of the doorway and the height about halfway up (so he can't scale it) and put hook and eye closures on the other side so he can't reach them and unhook them and push the door down.
I don't think your Mom coming and you staying up all night for a week will do anything, quite frankly. You need to do something LONG TERM as far as discipline and letting him know that he CAN NOT kepe getting up out of bed and roaming around the house getting into trouble. You have to show him that HE IS NOT ALLOWED to wake his sisters up, HE IS NOT ALLOWED to roam around the house in the middle of the night, HE HAS TO STAY IN BED for the night. Same thing goes for the other kids----when they wake up, THEY HAVE TO EITHER STAY IN BED, OR WHEN THEY COME TO GET YOU THEY HAVE TO GO BACK INTO THEIR BEDS BY THEMSELVES. I don't think this is a sleep issue, to be quite honest. People wake up during sleep all the time, and they fall back to sleep without getting up and going into someone's room only to be walked back to their own room---when they come in your room, tell them to go back to bed, and THAT'S IT. If they want to come into bed with you or sleep on your bedroom floor, then fine, but make it clear to them that you are not walking them back to bed. If your son is afraid at night, then let him know he can sleep in your room, but you are not going to lay with him until he falls asleep.
You have to get your rest too, or else you are going to lose it! Kids know what they can get away with and what their parents will do in response to their behaviors. I think your son knows exactly what he is doing, because he is doing a lot of purposeful movements and actions and involving his siblings. He is totally awake and wants to get into some mischief! He knows he can do this because you sleep like a rock at night! Make it so that he can't do this. He'll probably protest when he can't get out of the room for the first few nights, but he will learn in a short time that he can't do what he's been doing.
If you stay up all night and sleep during the day for a week, that is going to screw upi your schedule and your body, and I don't think it's a good idea. Going from night sleeping to day sleeping is very difficult, even for people that work at night for a living. Plus--it will still be difficult for you to stay awake at night in a quiet house, and if you watch TV or if your son knows you're up, he will probably come out of his room and want to play!
Just my opinion.