I'm a little late replying but thought I would add my 2 cents
I also have all the kids sleeping in the playroom ~ with the exception of one right now who just joined me and that one is 12 months in a fold and play and still getting used to nap time.
I thought it would be hard getting the kids to transition to a asleep mat but it has just taken me a week to get them into the routine. They are already used to nap time and know the schedule. When they get up and roll over instead they sit up to look at the toys, I tell them it's nap time and lay them back down. I have been lucky that I don't have to give any of them a mean look but I don't transition them around the age of 2- or if they are good sleepers and I've had a few, I transition them sooner and I haven't had a problem.