rat keeping food from cagemates

So, I adopted four brothers, all five months old a while back. Two have since passed. But, before they did, they both struggled to keep weight on. A third boy is also very petite, but not as unhealthy as the two brothers I struggled to keep weight on were. I thought, because of how sickly they had been, they struggled to keep weight on because of pre-existing health problems.

Syl just keeps getting fatter, though. At first, I thought his sudden gain was because he hurt his foot a while back and had to be less active for a while, but now I think it's because he's keeping food from the others. I think that's why my two that passed struggled so much with weight, no matter what I fed them. And I think it's why Merlin isn't thriving in the cage with his brother anymore.

Is this normal behavior? For one rat to get so selfish with food (even when I feed plenty for both) that he prevents cage mates from getting enough to eat? Has anyone else had this problem?

I'm going to start separating them at meal times, but this whole situation seems weird to me and I'm wondering if anyone else has had similar struggles.

I've had a few rats like that and what I did was separate areas during feeding and I would also hide blocks in certain parts of the cage. I would also find all the stashes and move them around two to three times a day. This one rat I had Simon, he was food aggressive so I would hold him while I would put fresh food in the cage. He had to wait in my arms while his buddies ate. I stroked him and made it a special time for him and I and he would get his share after the others walked away from the bowl. After a couple of months, he was no longer food aggressive.

I can start trying that with Syl. I can't believe it took me so long to realize what wad happening. I hope I can fix this and make things better for him and Merlin.

As of right now, I have started putting food piles on different sides of the cage and trying to watch them, but they don't seem to have any problems when I'm around. I think it's when I go upstairs that they do it.