I lay in bed with DD while her & DS go to sleep. Everyone goes to bed between 7.30 & 8. All lights & TV go off.
Big girls are easier, coz they share a room & put themselves to sleep. DS & DD3 share bunks & the only way DS will sleep in there is if I lay in there til he's asleep. He still ends up in my bed most nights. DD does every night, but I get a few hours to myself.

Maybe work on the younger ones first, then the older ones straight after if you can't get them down at the same time? Just make sure you set a bed time & stick to it.