If you have a restless sleeper, one that is not sleeping through the night there are a couple of things you should consider.
Do they still nap?
Naps are important and this article gives you an idea why. But just because they are important doesn't mean that you are using them properly.
Have you thought about removing the afternoon nap?
When my now 3 year old was 2 he started going to bed later and later, he would sleep maybe 8 hours at most at night and a 2 hour nap.
We cut out the nap and now he sleeps 12 hours at night.
My 5 year old was taking naps until she was 4, and still enjoys them, right before she turned 3 we cut her naps down to 30 minutes, she would sleep 10 hours at night with a half hour nap. We couldn't cut them completely out, she would get cranky after preschool and we had to give her cool down time. Each kid is different but they might benefit from a quiet hour in the middle of the day and no nap.
We learned pretty early on that she just needs less sleep than most. She gave up her nap between 12-14 months and we were much better for it. Without a nap she plays hard all day and usually goes right to sleep after bath and book.
On day care days they let her nap which makes sense for their needs but we pay at home by having a disruptive 2 year old who won't go to bed until 10 pm.
Your sons sound like they just aren't tired which makes sense as they are three years old and are probably ready to start giving up day time sleep. It might be worth trying to reduce naps to a 20/30 minutes nap followed by quiet time play, or give up the naps altogether and just do quiet time. Less napping should result in tired toddlers.