By attempting to force you to choose, your husband is doing the same thing to you that your parents did to him - and isn't that what made him mad in the first place?
He doesn't have to like them or forgive them, but it's not about them - it's about loving and supporting you and the children you have together.
Your husband needs to knock it off and keep his hostility to himself. You should go ahead and take baby steps (as suggested already) to introduce your parents and children so as to build a grandparenting relationship between them.
Family does matter and the fact that you are being the bigger person and attempting to forgive and put the past where it belongs is something your husband should admire and encourage.
Take it small, take it slow and good luck to all of you.