The best way to get a bird to like a second person is for the person the bird does like to "introduce" them. If your dad doesn't mind taking the time to do it that will work best. Have him spend time with the bird with you near. Your dad should show that you are friendly as well, maybe touching your arm while talking to or rubbing the bird. Having you hand the bird a treat while you are all spending time together. After the bird seems to be accepting you being around while spending time with your dad then he could try leaving the room while you are in their with the bird, especially if you have a t-stand etc to place the bird on, then he can leave the room and you can give the bird a treat and talk gently to him. Your dad can come back in after a minute or so to shown all is fine, gradually extending the time he is out of the room.
You can also work with the bird by yourself in a closed room. Let him come out of the cage on his own, offer him a treat if he will take it and just spend time in the same room together. If you have a treat or toy he likes he should come to check it out on his own. Just make sure to not make quick movements or loud noises to startle him and make sure you are the one to feed, give treats and clean cages so he is used to you always being there.
Some birds are a one person bird and they will sometimes form attachments to the strangest people. We have a timneh that fell in love with my nephew and although she will tolerate others she goes nuts when she sees him. He will spend time with her but is not overly into birds he usually likes working with the reptiles instead but he will spend time with her as well.
As far as plucking, does you bird have a wide range of toys, especially shreddables and "preening" type toys? If not make sure to make or buy some for him. TV's are fine for distraction but most birds like toys a lot more. If you notice he isn't playing with his toys as much then change them around, take some out put new ones in and move around the ones you leave in the cage. Try making foraging toys as well, even simple ones like a few treats rolled up in a brown paper sack. Having a "job" gives many pluckers something to do instead of picking their feathers. Also try not to pay too much attention to the plucking. If you go over and move his beak and say "oh stop that" each time you see him pluck he will know he gets attention for plucking.
Also if he hasn't had a vet check get one soon because there are also medical reasons for plucking, bacterial, viral and even poor diet can make a bird pluck more.
