So your intended is paying maintenance as well as child support. That would be very hard to swallow. It sounds like she may be having some mental problems. I live in Wisconsin and have had experience with someone paying child support in Minnesota. I think the top percentage of wages based on the number of children tops out in the mid thirties, unless the laws have changed.
Are the children safe with her? It doesn't sound like it. Is your soon to be trying to get custody? This does not sound like she is your "average" woman, but rather one with some serious problems. Is she employable? Or is she in a state where no one would hire her anyway? Remember you are stuck to this woman for life when you marry her ex. Make sure you are up for the challenge by educating yourself about step-parenting and parenting in general, because if she is troubled more of the mothering will fall on your shoulders if she can't or won't manage it herself.
I mentor two girls for Kinship, they are sisters and in the custody of their father. Their Mom is deeply troubled and simply does not have the ability to parent, so much of the mothering of the girls falls to me. I encourage them to have as much of a relationship with their Mom as possible and I sort of pick up the pieces when its not working well.
It seems to me that you are a very caring sort of person and that will serve you well and be a tremendous source of strength for your soon to be step daughters. An important thing to remember is that you must separate your feelings about the Mom from your daily life. I know that sounds impossible, but it can be done. When you are angry or upset, take a moment to analyze your feelings to see if they are valid. If what you are feeling is about something that you can do nothing about, toss them out - the feelings, not the kids (hee hee). With practice and determination you will gain control in an emotional situation.
Preserve your own dignity at all costs. Quiet strength. Be a safe haven for the kids and for yourself. If she wants to waste her precious energy yakking on the phone, that is her loss, because you will be busy building a relationship with her children. The payoff for all your hard work will be great I assure you.
Thankyou for letting me share what I have learned, much of it I learned the hard way and it feels good to be able to use it to help. I would be pleased to be a counted among your resources in this. I live in Western Wisconsin, pm me if you want more infor or a phone number. If you live in the twin cities area we are only an hour apart.
Deb