Sounds like you've been very fair. All I can suggest is to let him suffer the consequences of his decisions on this one.
Maybe you could try setting up family routines so to speak for everyone for a while eg. we all get up at this time (except maybe the little one), we all do this at this time. It might encourage him to know he has to be up then???

I really don't have much advice on this one sorry. Big though. x