> One point that may be lost in all the comments, [...] this was his father's company to begin with.
I've pondered this. There is no disputing (and I try to make this point in the paste) that my father actually brought something to the table. In this case, it was inventory and supplier relationships.
In some respects, the whole thing was so separate from the original company that I used to joke with my father that I should just have the money deposited in my bank account instead of his, and he should just give me a slightly better price on product.
We even discussed changing the name of the company when we transitioned to online-only sales. But, hysterically, the company is named after me, so I argued that it should stay the same, and eventually persuaded him.
Of course, it could be argued that it was a new business when it exploded on the internet after near-bankruptcy, however, it could be argued the son was just "helping the family business," as their was no formal business agreement (it sounds like). This may be a tough legal battle to get really anything, and sounds like your father would fight it tooth to nail; it may be a a very long road that you don't want to go down.
IMO, you might do better just continuing to help out here and there (as you've got things pretty well in shape it looks like), and distance yourself somewhat both emotionally and energy/work-wise. Lighten up just a bit about it, and you'll likely get 50/50 anyway, when your Dad is ready to stop working/retire. This way, you have a better chance of not fracturing the relationship as well, and it allows you to sort of emotionally unwind.
Yes, continue to be the break/fix guy and the architectural/platform guru as needed, but don't invest that kind of emotional (and actual work/cycles) energy anymore, if you can possibly help it (obviously this will be difficult given the history and attachments etc). Sort of unwind yourself a bit, and I think things may just naturally work out.