Its really hard for a Son in most cases to stand up to their father... It just is, however that dosent mean this guy has to take his crap too.
Your right in the fact that 9/10 when you stare guys like this down, they back off. Than they want to be your buddy and just move on to the next easy target they can find...
I grew up in a single mother household, so I do not understand the concept of son standing up to dad. However, if and when I had a child, and he was at his adult age, and he came up to me professionally and told me to back down... I would admire his courage for standing up to me.
Then again, I am not the type of person to insult someone and imply that I can do better because of his reputation. Seems like he is projecting his own ideas of how a band should work into your band and as many have said, that can be very hazardous.
TO THE OP: Perhaps, before a practice, sit down with the man as a band. See if the son will speak up first to him, but if he does not, try and reason with him about the situation. Tell him that you do appreciate his input, but do not comment while in the learning stage of a new piece. If he has a criticism, he is an adult and should address it properly with what he did not like AND what he would SUGGEST to resolve it. That should not mean that you should do exactly what he says. Take it for face value, and perhaps sample the idea with him, and ask if that is what he meant. Try it with the song and see how you like it. As the bass player, the bass is your tool and should represent what you think and feel should be contributed to the song. This should only be up for debate when it is the other band members have a criticism.
He seems like he has a lot of knowledge, and he could just be preparing you for the real world. Managers, booking agents, producers do not always care about the band on a friendly level, and just view what they do as work. Perhaps him breaking chops is a subtle lesson to learn to a) accept that there will be hardcore critics and that you will sometimes just have to deal with them. b) learn to stand up for what you do as your passion. If you make it big, kudos, but playing for fun and the joy of music is of utmost importance.
Playing in a bad mood and under pressure can result in haphazard playing as you can not focus on the groove.
So the best route might just have to be with talking to his dad. Go to the next practice, see how things turn out. Ask the guitarist if he would say something, or ask the guitarist if you can say something, but proceed only with respect. This could be valuable because when irate people yell, and see that you are remaining as cool as the Fonz, they will realize that there loudness/tone have little effect. Just be prepared for the worst case scenario which can be him trying to getting louder and more insistent. When bully realizes his most powerful tool (to seem threatening) is not working, the may up the ante, but it should decrease.
Goodluck!
