When I re-married and came in contact with Beloveds grandchildren I admit I was quite wary of getting to close to them, especially the girls. With all the stories going around at the time, 2000, of child abuse, I was worried if one of them took a dislike to me, they could come out with all kinds of stories.
I was lucky, we all got on fine, and still do. Now I'm simply treated like an ordinary granddad, even my suggestion that the elder ones use my name was turned down by them in favour granddad.
Maybe your husband has similar thought. Try talking to him.