I concur with the people who recommend giving this campaign a swift, epic end. Get those heroes across the finish line of victory, have a parade and a medal ceremony, and they all live happily ever after.
That cuts the baggage and allows you to move forward.
Next, if you wanted to continue DM-ing for the group, I would sit down and figure out some principles to govern my behavior. And I would scrupulously stick to them. Here are some of mine:
“No reasonable request should be unreasonably refused - and no unreasonable request will be considered.”
“If there is some ambiguity in play, and it is my fault for not being reasonably clear, I will resolve the ambiguity in the players’ favor.”
“I will only roll dice when I am not certain of what happens next and I will abide by the die roll. No die roll will be ‘softened’ or ‘hardened’ just because I want a different outcome. If I wanted a different outcome, I shouldn’t have rolled the dice.”
“The game works best when players make decisions and drive action. The game does not work when the characters are unwilling to go on adventures or seek fortune and glory. Characters that aren’t interested in adventuring are not playable and not allowed.”
“When PCs engage in hostilities with one another, they get to choose their opponent’s result. In other words, your character can throw a punch at my character, but my character chooses what happens as a result. And if my character casts a spell on your character, you say what happens as a result.”
“Play time is for play, not rules disputes. If I make a ruling, that stands until we discuss it some other time. Even if my ruling is wrong. We don’t stop the game to fight. It is wrong to steal time from the other players.”
“There is no game rule that solves a personal problem.”
These are a few I use to keep my game clean and fair. You might have different concerns and different rules. But starting with some principles and sticking with them can help you and your players with all kinds of issues.