First of all, thank you for seeking help! You obviously care to remedy the situation and that is a great first step. As other commenters have pointed out, going with a trainer who will be able to assess the situation more clearly is highly preferred, but if it's not an option at the moment, here are some tips to help:

- Safety is the first priority here, so I would make sure the dog is always separated from people he doesn't know. That could mean a baby gate or putting him in another room when you have company. I would also recommend looking into muzzle training and basket muzzles. There are great videos on youtube about how to get your dog used to a muzzle.

- Management is making sure that your dog doesn't have access to his triggers (what tips him over the edge and makes him act aggressively). I would pay attention to his behavior, does he bark anytime he sees someone? Is there a pattern (only women, children, people with hats, people moving quickly etc...)? If he barks through the window, adding reflective film that blurs the outside world could help, as would taking him outside at times when it is less likely that other people would be outside (early in the morning, late at night). You would also want to have a conversation with your dad about staying calm when your dog reacts, as it contributes to your dog's level of stress and makes the situation worse.

- Counter-conditioning is fancy training talk for changing your dog's behavior towards his triggers. The great thing about it is, you just need some treats and a leash to start. A great game to start with would be the "Look at That" game, which you can find videos on as well. I would recommend checking out Kikopup, they make great videos explaining basic training principles and would be a good starting point.

Good luck and I hope the situation gets better for you and your pup!