I have a few ideas. First of all, I am a HUGE fan of sleep sacks. If you are not familiar, they look them up online. Basically a sleeping bag with arm and neck hole. I use them for all my pnp sleepers so that I am less worried about climbing out and they are cozy and warm.
Is there a way the 11 mo could sleep somewhere else? I hate that I have cribs in my own bdr, but it's worth the sanity! He should by all rights be taking 2 naps per day (and so should the 14 mo, usually).
I would lay BOTH the younger kids down at 9 for a 45 min nap, earlier if there is any eye-rubbing before that. You can't make them sleep, but you can put them in their cribs. A sweet cuddle and a kiss, then night night. Put them in and walk away.
I am not a fan of all the music, etc, although some sort of noise barrier might keep you sane until they get the hang of it. Maybe play the soothing music in the room YOU are in...lol.
After 45 minutes, give some sort of outward signal that nap is over. A loud song, make up a chant, whatever. Go in and get them up. Maybe even make up a chant and have a "it's time to get up" parade with the older kids. Just do it the same every day for a while...both naps. If they wake up before the chant and cry, don't get them. They can wait for you, crying or not. You can't control that part. If they ARE crying, talk soothingly, but say "I will get you out when you stop crying".
I would do afternoon nap the same way for the toddlers, at 1:00 ish. They should by all rights sleep 2+ hours!
For the older ones, I would allow them each to pick one book (or maybe a quiet toy if they're not book kids). If they are quiet, they get to keep the book. If they get up, they LOOSE THE PRIVILEGE of the book. Also, sleeping with your friends at the super slumber party we have every day
is a privilege. If you get up, then you get moved away from the group. There rest time could be 1-3, sleep or no sleep. Chances are with a book and a little boredom, they'' be asleep pretty fast. Again, can the music, but dim the lights.
In 2O+ years I have rubbed very few backs-maybe for a minute or 5 while a child was transitioning to daycare, or once when I had a child that was really, truly neglected. I have good, happy sleepers here, but they haven't always started out that way. But, sleeping is not a punishment...they are so LUCKY they get to take a nice, cuddly nap in the afternoon. I think a lot of kids get the message that it is some sort of horrible thing we do TO them....
Good luck!