Hello Olympia.....Good morning. It is unfortunate but somewhat understandable that you have accommodated this rift for so long. I would try the emotional blackmail bit by stating what I REALLY want for Mothers' day is ......... the time and place to be chosen by you, of course. I would then state categorically that I do not wish to know in advance who's coming. 'Just turn up if you want to be with me, please'. Now this may end up with only yourself and the 'uninvolved' son. So be it. Furthermore, it may end up with you ON YOUR OWN. MENTALLY PREPARE FOR THAT, Olympia and the outcome, when known, could well have positive consequences. Either way, you've tried. What more can a Mum do? We just go on loving with the edges getting more frayed by the minute. I feel for you. My ties are not brilliant but I don't have specific problems. Good luck.
Parents-in-Law. What do/did you call them?