Your ex sounds like she is expecting you to wash your hands of your daughter. 17 is nearly an adult but NOT an adult. She sounds young and troubled, so kudos to you for wanting to help her. The woman (ex) needs to accept you are a parent first, boyfriend second. GTFO if she can't handle this, which is sounds like she did. You will have less drama in the end for it, I think, so don't worry.
Of course, helping doesn't mean 'fixing'. Your role as a parent, especially at this age, is to help facilitate your daughters transition to responsible adulthood. Which might mean allowing her to take the consequences of bad decisions (within reason). If you aren't sure what this means, I think Wakeups suggestion of some family counselling is a good one.
As for your son, I think I will leave comments to the more experienced parents in this matter, Vash and Qwerty.
Best wishes for your family.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh