I'm curious how many Anglo/Euro merchant families' wealth didn't involve slavery.
Let's see: The Waynes came over in the "colonial" era. (canon). They are Old Gotham City Money. (canon). Gotham City is an east coast city. (canon).
I think we have to assume that the Waynes were originally gentry rather than related to royalty--there'd have been stories about Bruce Wayne's royal ancestor if that were the case.
I could bore you about what position the Wayne family must have taken during the English Civil War, and why that matters, but I think I'll leave this here