Nap time challenges

It's crucial to our survival that both kids nap at the same time on weekends.  The problem is that Alice usually isn't ready for a nap until 3 or 4 pm, and Simon typically takes naps at school at 11:30am.  So we usually just try to stretch Simon out as long as we can, then put Alice down a half-hour later, somewhere around 2pm.  Some days Alice doesn't nap though, so now we just require that she at least stays in her room. She can sit on her couch and look at books, but she is supposed to not shout.  She is actually pretty good at doing this, and sometimes she will eventually fall asleep.