Thanks for your input! I set up the room so the 1.5yo and 2.5yo will go up to nap together, and hope for the best. I don't have nap mats for the 3 older ones. My 3yo has gone upstairs with her sister on occasion if she needs a nap, but prefers to stay up with the boys and go to bed early. I'm going to try getting them to do yoga on an area rug followed by guided visualization, and make them stay laying for 5-10 min afterwards. If it works I might buy some mats and have a progressively longer down time.

The 2 oldest boys will start school in the fall, but our province doesn't do JK, so they turn 5 this year, and don't take any rest/nap at home.