@Blueberry pie, if you do read back a bit you will see that most posters simply advise the OP to not upset the apple cart, to try to see her son and GCs separately and not to say anything critical to him about his partner/wife. Am not sure, based upon information given, that anything else can be advised.
The issue is that some tend to judge all estranged parents as somehow being the only ones at fault and so it is incumbent upon them to take whatever is dished out to them and consider themselves lucky if their offspring one day decide to actually treat them like human beings. I know this personally, it has been my experience for many years, and at this point in time I will say that I don't mind criticism, bring it on, but if I want to be judged will wait until I am in a court of law before that happens, nobody has the right to judge others unless they have walked in their shoes.
Is true that some EACs have a dreadful time of it and have to estrange from abusive parents, my heart goes out to them, and their parents are entirely at fault. I don't think that is the case with the OP on here, though as I say we can only advise on information given. In my own case my DH and I were abused by our eldest daughter, 'yes', we can also be abused, it happens, and couldn't break the cycle until our other three daughters, already estranged from their oldest sister, intervened. Not early enough to prevent me suffering a breakdown.
So you see there is a backstory we don't know when parents/grandparents come on here to seek help and support, some despairing and in poor mental health as a result, so it is wise to keep that in mind also for this is a support thread and we don't ever know how fragile people are who seek us out. Many don't return when criticised heavily, or even abused by visiting trolls.
Everything needs to be put in context, and I hope this helps do just that.