D.M.
His behavior may have NOTHING to do with his folks keeping or not keeping him on a schedule.
Our oldest is growth hormone deficient. He didn't have any odd self-soothing behaviors, but he almost never had to SELF-sooth. I ended up co-sleeping with him originally because it was the only way I could get ANY sleep. He just would NOT go to sleep. He was up several times a night, he went down late, and woke up early. He hardly ate. It didn't matter WHAT we did as far as trying to schedule him.
He has NO developmental delays - he just didn't NEED to eat or sleep because he was growing so slowly. His GHT (treatment) started at age 4. He is now 6 and sleeps, most nights, from 8 until about 7, just like most kids his age (*relief*)
We also have an adopted son who does rythmic head banging when he is frustrated or tired.
Both of these boys are wonderful, happy, and bright.
Our third son sleeps fine. But he is up early!
Do what you can, but you may want to ask the parents about this as well. As there may be something going on other than not enough sleep.