N.N.
Hi K.,
I was your daughter many years ago, and I knew it all--didn't we all? But I can tell you what DID NOT work that my parents did. They did as one of the replies suggested, they cut me off. That was the absolute worst mistake they could have made. It only made me feel MORE dependant on the loser that I made myself look past all of his shortcomings and thought that he was the best thing for me. Even worse, when you are a very young mom like that (I turned 18 a month after my 1st son was born), you start to think that no other man is going to want to be with you because "no one wants an instant family."
So, speaking from real life experience, when your parents--those whom you've grown to love and depend on in times of need--suddenly cut you off, you get the message that you have no other choice but to stay in your status quo. I think it would be a HUGE mistake to cut her off and only do things for the grandbabies. That will also send her the message (again, speaking from a world of experience) that you love the babies, but now that they're here, your daughter is worthless to you. You don't want that, especially if you want to change her situation.
I would suggest just loving her, sticking by her side, and possibly only occasionally showing her examples of what real love looks/feels like. When you're a young mom, you start to have a low self-esteem, and you think that possessiveness, etc is love, and you feel lucky that the father came back to you after he left you, or threatened to. The absolute best thing you can do is to build up her self esteem. Be there for her if she needs someone to watch the kids, encourage her to keep herself looking and feeling good. I know that my loser ex husband always got irate if I put makeup on or did my hair, especially if it wasn't to go somewhere with him. Now looking back I realize that he knew that I could/would find someone else, but back then I thought it meant he just really loved me a lot lol. What I'm trying to say is that you need to help her realize how much she is worth and find a loving way to convince her that he doesn't have to be the end of the road for her. But you have to do that in a way that isn't pushy or bossy because at her age, she's only going to run harder in the other direction.
Good luck!!!