Clarification requested....As a former LEO, let me give you my perspective. When an incident is occuring, you need to call the police and they need to arrive before you get there. It is their job and responsibility to maintain order and deal with unruly subjects.
Arriving at the scene and trying to handle it yourself is just asking for trouble. Eventually someone will be injured or killed. Up to now you have been lucky that one of your uncles friends hasn't pulled his own gun.
If you arrive and the police still aren't there, wait in your car until they do. If one of these guys trys to attack you in your vehicle, he is the aggressor and you are justified. If you jump out of your car to confront him, that makes you the aggressor.
It's time to charge this guy with trespassing, appearing drunk in public or disorderly conduct.
So lets say for sake of argument that his father(albeit foolishly, but none the less) has called the son for help rather than 911(lets say easy speed dial or something). Son hangs up and calls 911 and heads out. Son arrives, knowing full well dad is in danger, yet the police have NOT arrived yet. Do you still expect him to sit in the flippin car?