I've never given any of my kids a bedtime snack. Is this a thing? If a kid is hungry at bedtime, I imagine that he is either not getting enough food during the day or is stalling. Going to bed hungry will, if given enough time, likely lead to the child eating more the following day.
It will probably take a few days or a week to break through the cycle that has been established. The child is not likely to starve in a few days. I'd tell the kid, "you're hungry for breakfast, so you'd better get to bed so you can wake up and eat tomorrow."
Then be sure to serve a big breakfast with lots of yummy food choices (fruit, protein, dairy, grains, even veggies) so that they can really learn to fill up in the morning and look forward to breakfast.
My older two shared a room from ages 18 months & 3 yrs, and I guess we were lucky or I have a bad memory, but I can't remember any major sleep disruption issues. Then all three of mine started sharing a single bedroom at ages 2, 4, and 6, and again, no major issues. They had the same bedtime and wake up time as each other, as do yours, although our times were earlier. But if you keep rock star hours, as long as they all keep the same hours, I thing that should be fine. Good luck!
Edited to add: We also used a white noise machine for a while. Seemed to help pacify at bedtime.