Amy makes a great point. Getting on a set schedule of visitation time will help in a lot of ways. The girls will know when it is their time to spend with their mother. Maybe that will lessen the last minute phone calls to ask D13 if she wants to go to dinner. That way, nobody has to avoid taking the phone calls. I know you will encourage the girls to work on their relationships with W. They, however, are old enough to speak up for themselves. If they don't want to spend time with OM then they should get into the practice of asking their mother who will be there. They are going to have to figure this out between themselves.
More importantly, a set schedule will free up time for you to get out and get the proverbial life going. The possibilities are endless when you don't have to worry about being home to take care of someone. You will be a part-time empty nester and trust me, there are some positives to that!
I think your interaction with W was mainly good. I know you are trying to regain your Alpha Male. One suggestion: try to resist the urge to throw in OM or her relationship with him during your conversations. You would have made your point by simply stating "I don't care what you do." Let her fill in the blanks.
Regardless, get on a schedule. It will make all of your lives easier.
Hugs, Spitty
Always do right. This will gratify some people, and astonish the rest. Mark Twain