Well, I definitely would not recommend SITTING anywhere near a steer that is even remotely not well-behaved. This would put the person in a very bad situation very quickly if things escalated.
Something similar is happening with my steer (he's not for show, but still needs to be a nice boy). He is okay with the man that feeds him when I am not there, he is NEVER ok with my husband. In fact, just the other day, he decided to push my husband into the hay
I shouldn't laugh, but it was funny. My husband went to 'bop' him on the nose and Buddy decided that wasn't going to happen. I spoke in a stern voice and I bopped him on the nose, not very hard, but he knows that when I do it, I mean for him to stop and behave. He doesn't try anything with me.
Did you ever consider that he was/ is trying to protect you? Just a thought.
I wouldn't suggest having any other person try to correct him besides you because, well, I really don't have a reason, but it seems to be working for me and my steer.
What about your dad offering carrot slices or other treats? Move slow, but quick work with him, but don't make him too anxious. Treats are a good way to get anyone to behave. Can your dad walk past him? Try having your dad get closer and closer, maybe even just brushing up against him at first. I wouldn't involve any friends until he is used to your dad, and be sure to explain to your friends, when and if you decide to involve them, everything about your steer, the risks, why you need their help, and how they need to act around your steer.
Good luck and keep us updated!!!