M.H.
That is a hard situation to be in. If your husband wants to forgive and make up let him!! If anything ever happened to his dad and you had prevented him from contacting him to make amends he would resent you big time!
I would just try and keep peace as much as you can for you kids sake. Your husband will get the hint if his dad isn't interested in making up and he will feel better he took the high road and tried.