Hi there,
I don't think your OH has any relevance on whether you have twins - though it would affect whether your offspring has twins - i.e. it's you that has to either release 2 eggs or have an embryo split - not him - but he can pass on his genes to your child. Your Grandfather could affect your chances though. It depends on whether they where fraternal twins or identical twins. Fraternal twins hare heriditary and identical twins aren't. Other factors that affect your chances are if you are above average height or weight, >35 years old and had children before...
Hope that isn't too confusing
Han x