At this point he is a "teenager" and teens can be very impulsive and silly. I think Bwilson made some good observations and suggestions. Also yelling at your dog when he's barking just takes the chaos to the next level. Our new rescue dog has just started to bark at passing people and dogs (we've had her for 8 weeks). I will check to see what the fuss is about, tell her she's a good girl, then gently lay my hand on her back and shush her. Work in progress, she's trashed a couple of plants lunging for the front window, but we're all learning
As far as your dad goes, maybe you could convince your dad to give your dog some treats everyday so that they become more comfortable with each other. I'm sure your boy senses your dad's anxiety and is reacting to that. Dogs are very sensitive to body posture and facial expressions, they are better at reading humans than humans are at reading dogs, usually. So your dad's paralysis might be feeding into the situation as well.
Basic obedience training is a must, and maybe you can check into therapy dog training as well. Some of that involves the dog becoming comfortable with wheelchairs and canes and so forth.
Good luck and keep us posted!