Hello!!!

I recently went on Vacation and left my sister in charge of my gliders. Since I know they play with each other I didn't ask her to play with them as much as I do. I had just got mine neutered and I noticed he had a lot more energy. And that's great!! But, when I got back I noticed my other, more submissive, male was small, skinny and almost NEAR DEATH. Turns out my other male was stealing food from him. My other male looks fine. Fat even. Whereas my other barely has the energy to chew. I gave him some apple and noticed he could barely chew. So I made him some scrambled egg. I have him in a smallet cage and in my room so I can keep an eye on him.

What do I do and what can I do to keep him safe and to stop the other from stealing?

I'm no expert but I think you should have more than one bowl of food in the cage. Make sure the bowls are far from each other. This will make it harder for the male to steal all the food.
Until he gains more weight you should feed him separately.
I would highly recommend taking him to the vet.

What diet are you feeding?

how much are you feeding them?

are you sure your sister fed them?

did you check to see if he was dehydrated?

do you know how to check to see if he is dehydrated?