I came here to say separate blankets too. Employed this approach not 2 weeks ago with 5 and 8 y-o. Eventually 8 y-o decided he wanted to sleep on the floor, which worked out great as well with a folded up bed spread under him. With their lighter bodies, kids need a lot less padding under them than us adults—thought you might have to sell them on the idea a bit. We’ve built cozy nests in an open closet before as well, too good effect.
I came here to say separate blankets too. Employed this approach not 2 weeks ago with 5 and 8 y-o. Eventually 8 y-o decided he wanted to sleep on the floor, which worked out great as well with a folded up bed spread under him. With their lighter bodies, kids need a lot less padding under them than us adults—thought you might have to sell them on the idea a bit. We’ve built cozy nests in an open closet before as well, too good effect.