I read through the full version. One point that may be lost in all the comments, that I think is salient, is that this was his father's company to begin with. The son helped the father bring an internet presence to the business (eg, go the business online). Yes, the father took advantage and it's likely not ethical, it was still the business that the father started.

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.