Well he might be ready to commit to being part of a couple, but you seem to want him to commit financially to being a father and family man.
I dunno, it's a hard gap to bridge.
People who don't have children get to spend £1000 on music courses if they want to (and they have it). Parents don't normally have that kind of money to spare.
You seem to want him to have the finances of a Dad of 3, despite the fact that he doesn't have any children of his own.
Is he ready to be a stepdad?
Obviously he can't move in with you unless he is.
But even a stepdad isn't necessarily as financially responsible for his stepchildren as the parents are.
Is there a way you could organise his finances that would recognise that he didn't choose to have 3 children and never get to spend any of his money on himself?
I'm normally all about pooled family money, but it doesn't sound like you guys are there yet. Which doesn't mean you won't ever be...
TBH, given the children and their attachment, maybe you should hold off on setting up home together until you are all ready to become one family.