One of the worst investment in the world is being in a startup. It is extremly high risk, the reward is amazing when it works, but when it doesn't then it is extremly bad. Therefore, you need to be very careful where you put your time on.
When you know there will be a messy meeting and there is nothing you can do about it, the best thing to do is to avoid it. Messy people produce messy meetings, and they take the time and the energy of everyone who is part of it. That is why instead of being part of this drama, find a better team and better meetings to invest your precious energy.