Thanks for filling us in a little more SJP. I understand your reluctance to give too many details. However, that may be why I'm a little confused. Apparently, for some reason, your son has to have supervised visitation with his children (I realize that must be hurtful for you to know). If I've got this right, you've been approved to be one of those who can supervise his visits, even though your relationship with him isn't 100%. With all due respect that doesn't make sense to me and I suspect there must be a lot of tension during those visits. Am I wrong?
Anyhow, now it seems ithas been decided that your visits have to be supervised, too, by ex DIL, no less. Could that be partly due to the problems between you and your son?
Also, you say you now want to focus on "rebuilding (your) relationship with" him, "so that GC contact will be restored in due course." Are you saying that he has lost his contact, for some reason, and it has to be restored? Or are you talking about your being able to see your GC w/o ex DIL there?
You don't have to answer my questions, of course. But here's what I THINK you're saying - You've decided to stay away and contact your GC only by phone, for a while, if you can. During that time, you plan to work on your relationship with your son, so that, in time, it will be good enough that you can visit with him and your GC/supervise his visits with your GC on your own, w/o ex DIL being present. But maybe I have that all wrong.
If I'm right, t sounds like a good plan, IMO. It's hard to be with GC, much less supervise visits with one of their parents, when there are issues between you and that parent. I'm not sure what or how much it will take to repair your relationship with your son. Or what will be accepted as "good enough" and so forth. But I think you're on the right track and I wish you all the best!