Well C, would be my answer.
But if that was me, I would have stood up and said.
“well I have always loved you as my natural grandparents, but it’s obviously plan to see and by what you have said here, I have made a terrible mistake and you are not fit enough to be my grandparents, so good bye forever and shame on”
Then I would have walked right out of their lives forever. The world is indeed full of cruel humans, but you have a choice, those that truly love you, or those that pretend but repeatedly hurt you.