I think the easiest way to move on and forget them would be to get involved in something different that excites you and is successful. Find a new project or a new organization that requires more of your mental energy. Otherwise, I could see writing a letter to each of those board members and telling them what you think needs to be done and the consequences of mismanagement. That might not be possible if your kids and family are still involved and you have to be polite to them. But maybe you just need to point fingers and say what needs to be done. With a letter like that, you’d have said frankly what they all need to hear but you’d also be cutting ties. No going back after that so you must move on, kwim?
Im sorry you are going through that. I posted about a similar situation last year and unbelievably it resolved itself. But it took years before the change happened and then it has very slow been changing. A year later we have some new people in charge and they are finally steering the boat but time will tell if they steer it in a better direction or slip into the same rut the last folks were in. It’s been agonizing so I understand what you are going through.
" I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent." Mahatma Gandhi
"This is the ultimate weakness of violence: It multiplies evil and violence in the universe. It doesn't solve any problems." Martin Luther King, Jr.