How do you handle a difficult DM in D&D?

I am currently in a long-running game with friends and family. The question is, what do you do about an inconsistent and abusive GM?

Example: Recently mid-session, there was a routine turn of combat played out similarly to any other combat we have done in the past. During this one, however, arbitrarily the DM decided to change already ruled upon and established ways in which we did combat. When it was pointed out to the DM that a ruling had already been made by them in the past that contradicts their ruling now, and that we had been playing this way for the entire campaign, he refused to hear it.

This was then followed up by a simple statement of "We can discuss it later, lets continue". But when that was said, the DM took a harsh "How Dare You" type of stance, loudly berated the player for suggesting that it could be discussed at a later time, proclaimed that there would be no discussion as it was "already had", and made it clear no questions were to be raised on their rulings.

The player and DM then proceeded into a circular "I don’t want to stop gameplay, we’ll talk later." followed by "We will not talk later, you are ruining this whole session by questioning me" argument that effectively killed the entire night.

In this instance I do not know how things should proceed. Should we inform the player that regardless of inconsistency and contradiction to previous rules they have to deal with the DM’s decisions and the fact that they won’t discuss anything further at a later time, or should we confront the DM letting them know that they don’t have to bend to player requests/questions, but losing it over the "audacity" of someone saying they will talk about a ruling later is pretty crazy.

I know in D&D that the DM is ultimately the decision maker, but is it ok for them to change their own rulings arbitrarily, and to tell players they aren’t allowed to discuss it?

This is not a campaign we can simply walk away from as it is a family event, but how do we address a DM like this IF we should address it at all?