If your son skipped college to go looking for an apprenticeship immediately... does that mean he is buying into his dad's scheme? I know your X hasn't done anything for your eldest D, but that hasn't seemed to bother him in the past. Doesn't he see his dad isn't doing him any favors-- if your X can't afford the flat, how on earth will he?! Particularly since he won't be making much as an apprentice.
As some point your S and youngest D are going to start feeling seriously used. I mean, wow-- what sort of man plays his kids this way?! When the penny finally drops, they're going to be FURIOUS with him.
Is your youngest D moving back in with him now that she's on the mend, or will she be staying with you?