Step Talk

As most of you know, our Bm is handicapped. She doesn't drive, so her mother has been gracious enough to pick my SS at the end of our weekends. Our Bm is quite the control freak, and we're tired of playing games. What I mean by this, should there be a need to stray from our usual pick up/drop off schedule, Bm talks to her mother about a new time/place, etc, then calls my DH, she and DH discuss it, then she goes back to her mother, and so on and so forth....it's SUCH a hassle, and more often than not, she won't call back, or delay a call back and Dh has to call her and wait, etc. etc.
Dh has recently proposed (only to me, of course) that we cut Bm out of the picture, so to speak. Not in a mean way, but being that he/myself/and the grandmother are the ones doing the driving, it seems easier to speak directly. Obviously not for everything, but as far as pick up/drop off. We have learned that we can't control her behaviour, but we can find other ways to make it so she CAN'T do things that are unfair/annoying. For example, we can't stop her from not telling us about certain school activities, etc. but we can speak w/SS teacher and find out for ourselves.
Something along those lines....I'm curious if anyone else had experience w/something like this, or maybe wants to let me know their thoughts. I'd appreciate it!! Thanks