Grandparents do have rights. I don't know what your financial situation is, but if you can hire a lawyer you might be able fight to see your grandchildren.
On the other hand be glad you are out of their house. Send birthday cards to the children, call them on their birthdays, and discover that your son in law is not the only awful person. Your daughter married him didn't she? She bares some responsibility here as well. My advice is to get a dog or cat. It always makes a person feel better to love something that will love them back unconditionally. Good luck to you.