You poor thing, I really feel for you. Maybe try giving them a warm bottle of milk in bed might put them back to sleep or adding an extra blanket.
Do you always get up with them? Maybe if your DH gets up and puts them back in bed for a while the change might encourage them to stay asleep - because its coming from a differant source IYKWIM. Also you need a good nights sleep yourself occasionally.
Also maybe you could cut out the soft music - I read a study a while ago about music as a sleep aid (this was in adults but it may apply to children) which said that although it can help in getting to sleep people who listened to music while they slept had altered REM patterns so it may not facilitate a good nights sleep.