I'm sorry you're having this issue with your CAG, but there just isn't some easy or quick fix to this...This is an extremely common problem that has broken-up marriages, ruined friendships, ruined brother/sister or child/parent relationships, and caused a lot of heartache. A lot of the time there is one person in the household who actually buys the bird and is the only person who does anything and everything for the bird, and even so the bird chooses another person in the household as "their person", sometimes they choose a person who hates the bird and wants nothing at all to do with the bird...There's no rhyme or reason as to why they choose who they choose, and the only way to ensure that they choose you is if you live alone and are the only person in the house. That's about the only 100% way to make sure you don't have this issue...
As Wrench stated above, all you can do is make sure that YOU are the one who gives him all the treats, feeds and waters him, lets him out of his cage, basically YOU do anything and everything good, and someone else does everything bad, like Vet trips, etc. But even this will not make the bird choose you over your dad or even guarantee that the bird will start to like you.
***That being said, it's very unhealthy both physically and psychologically to leave a parrot locked inside a cage 24/7, he must get at least 3-4 hours minimum outside of his cage every day playing, flying, walking around, etc. So if he has a play-stand or a T-stand, or some other type of portable perch that he likes to sit on when he's outside of his cage, you need to try to just open up his cage and let him sit on the stand...Actually, if you are able to commit yourself to spending a good 3-4 hours a day with him, even if this means that you are the one who is just sitting in a room with him behind a shut-door so he can be outside of his cage every day for a few hours (and so no one else that is scared of his has to interact with him, as he knows they are scared of him, and that isn't helping the situation any), this would be a good place to start trying to bond with him...
If your dad isn't going to be home then that's the perfect time to start getting into a daily routine with him, where you take him into a room or you shut the door to the room his cage is in, and you do this at the same time every day if you can, if not then just try to do it at least once a day, and you let him out of his cage in that room with you in the room with him. You can do whatever you do, get on the computer or play video games, watch TV, etc., while he's out of his cage playing or flying, etc., you can also try to read books to him, play YouTube videos of parrots for him, and just try to spend a good amount of time alone with him every single day...and have lots of his favorite treats with you at all times...This will do two things, it will ensure he's getting a few hours out of his cage every day, and it will start the gradual, slow process of you hopefully bonding with him. It will be a marathon, not a sprint, as it's going to take a long time of spending this one-on-one time with him every single day, but if you actually do really commit to doing this every day, it's your best-bet to get him to open-up and eventually give you his trust...
