You will likely go through life with many jobs. You will only ever have one father. Lots of people would kill for the opportunity to have worked alongside their father for years, even exploited. It's special.

I think you have to decide how much your relationship with your father is worth to you. If you can put a price on it, make darn sure whatever you do next is 100% going to result in that price, or more, and you won't lose any sleep.

Consider for a moment that maybe your father did more to keep the business alive than you think he did, and that maybe you did less to keep it alive than you think you did. You're not crazy to think you're a 50/50 cofounder, but you're probably wrong to think it.

I think you should consider opening your own warehouse across town, doing the exact same thing your current business is doing. Build a better engine, and skim the cream your current business is getting (for the 90% of inventory that generates 10% of the revenues, simply send them the business to keep your new venture and cash burn optimally-sized). Don't clue your family into what you're doing. If your father is essential and irreplaceable to the business model, then your venture could fail. If you're the essential one, then you can gift your family some nonvoting stock after your business takes off and theirs tanks (assuming Amazon doesn't eat both your lunches in the meantime).

But consider this all with the backdrop of only having one family. You can't put a price on that, or at least I can't.