Well, your dog is definitely acting like a different dog when you are around. He may be fearful of your father and is acting to protect you when you are around. Most dogs are very territorial and will protect their pack. He may relax when you are not around because he doesn't feel the need to protect you. There are any number of things that could be going through that dog's head, but it sounds very behavioral in nature.

I am not a behaviorist and work mostly with medical issues in pets. Sometimes, sedatives are needed to start these guys on, just to alleviate some anxiety prior to working with them. Consider talking to your vet about what might be a good option for him. I highly recommend working with a behaviorist or dog trainer in your home. This will allow him/her to fully assess everything that is going on in the home and make solid recommendations to alter the behavior. Let me know if you need any recommendations for trainers.

Best of luck to you and Zero!