I have a hard time with the belief that you should just, "let it go!"
I suppose there are advantages to keeping silent about such behavior but for the life of me I don't know what those advantages are!
If your husband has the facts right, and he is sure of the situation with regards to his parents motives, he has an obligation to defend HIS family and HIS motives. If your husband can think it through and work his plan, he can undo some of the serious wrong done to you both.
Behavior rewarded is behavior repeated. Do not "enable" their wicked acts by doing nothing, thereby rewarding this behavior. I would not bother with the dickless Elders. Let them run to these window washer/ministers of a book printing company.