If this business's profits paid for yours and your brother's college education, as well as supported the family while you lived there you need to take that into account. You may also want to take into account that even according to your own version of events, your dad had been running this business since before you created the eStore. Plus there's a huge gap in the middle of your story (college + job + own startup) where you didn't work for the business while your brother and dad did.
I guess what I am trying to say is: You deserve equity but not the 50/50 you seem to believe. According to your own version of events (which paints things in the best possible light for you), your dad still did the majority of the work, took the majority of the risk, and was paying for things for you while doing so.
I think your dad's greed is affecting his judgement, but frankly I think it is affecting yours too. As an exercise go rewrite this story from what you think your dad's perspective is, setting out what he did, and how things will look for him.
Again, you deserve equity, and I have no idea what he already gifted you. 20-30% would be in the ballpark of fair. But in general I think you're seeing green a little and just want more power than your brother for later, which isn't a healthy place to come from.
You could go get lawyers involved but win or lose, you'll lose.