FOG - fear, obligation, guilt; three of the more damaging of many damaging legacies left by your narcissistic mother and her weak enabler of a husband who also needs someone to idolise. Narcissistic women cannot at all do relationships and the men that stay with such women either get booted out of the marriage (because she turns on them) or are narcissistic themselves. You cannot rely on your Dad to protect you from her because he will continue to side with her.
Do you think they feel or are wracked with guilt - no, not a bit of it. They are like this because they are dysfunctional and not the nice and kind parents you perhaps still want them to be or hope that they will become. BTW they won't become nice - ever.
They trained you well to subjugate your own needs and wants (you were taught that you do not matter) and put theirs first; its all inbuilt and they trained you from childhood to serve them and put you last.
Re your comment:-
"Also I just don't know how to proceed in the future as want some contact but problem is it's all near intolerable. And they make me pretty ill... I'd like a sort of don't contact me, I'll contact you arrangement..."
The contact you've had with them has driven you to distraction not surprisingly but FOG still wants you to have some contact.
Simply put re the don't contact me I'll contact you, that will not work out because they will continue to railroad, ignore and disregard through any boundary you care to set them. They have not listened to date have they?.
I think that ultimately you will have to go NC with them, also such people make for being deplorably bad role models as grandparents as well.
The last thing you want to do is expose your children any further than they already have to their dysfunction because you will in time kick yourself roundly for doing so. They are still narcissistic through and through, they have not changed since you were a child.
If you have another set of grandparents in the picture then focus on them. It is rare that both sets of grandparents are nasty. Emphasize to your children how much we enjoy being around grandma and grandpa so-and-so (the decent and loving grandparents). Cultivate your children's relationship with the decent, loving grandparents. Teach your children to be grateful for the decent, loving grandparents. Gratitude is a highly effective antidote to loss. Focus them on what they have, not what they don't have. Model that attitude of gratitude.
I would also now block their number from both your landline and mobile phones. Same with e-mail. Sounds drastic but it will help you going forward.
You owe them nothing really. They have abjectly failed you, not the other way around.
I would also suggest you post on the Well we took you to Stately Homes thread and read the website entitled Daughters of Narcissistic Mothers.
"Will I ever be good enough" by Karyl McBride and "Children of the Self Absorbed" by Nina W Brown are good reads.