Take heart! We had the same situation in our pack several years ago. Dad became Cubmaster then den leader, Mom became den leader, Step-Dad became Committee Chair. The oldest son is now a scout and doing well. The second son is one of twelve Weblos I, Dad is his den leader. Next year he will be with Mom. She is leading the fourteen Weblos II den.
If they do not settle this in private, settle it for them by asking that they all step aside for the good of the pack.