@Smiles estrangement is often unfathomable, despite some trying to cast blame upon the easiest targets - the parents of the AC of course. That is not only too easy but also lazy.
Luckily - and that might sound harsh - my DHs father died early when he was still very young, if he had lived longer and carried on abusing my DH I imagine he would have become estranged from both his parents.
In this case an estrangement is understandable, but because his mother had struggled to raise him on her own and muddled through despite increasing ill health from her mid forties my DH always looked after her even though he couldn’t forgive her for his earlier years. I similarly helped look after her and our children loved her dearly. It truly made me sad when my DH said that she had never loved him as a child the way she loved our children. Perhaps she saw it as a second chance.
In any case we have happy memories of her spending time with the children, it enriched their lives as a good relationship with grandparents can. To deny that to your children who have no say in the matter and then imagine you are a better parent than the parents you estranged is sheer hypocrisy.
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. Knowing that despite what he endured as a child, that he with your support was still prepared to be there for her in her old age and enabled her to be a GM to your children makes so many cases of estrangement even more unfathomable. 
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. I'd be tempted to leave a few nails lying around where he' going to park and hope he gets a puncture; maybe one in each tyre with a bit of luck.
Reducing contact because my heart just isn't in it.
