Higurashi and Umineko take place in the same story universe as far as I'm aware, but there is no character overlap. As of Umineko, there is an entirely new cast of characters. That said, events in Umineko may shed some light on the workings of the Higurashi / Umineko universe, and it references Higurashi quite a bit.

While it is not strictly necessary, I think you would get more out of Umineko if you watched Higurashi first, even though the cast and story is entirely different. Also, if you can manage, I'd recommend reading the Visual Novels for Umineko instead of watching the anime. The anime is poorly done and ends prematurely, leaving you with far too many questions unanswered and no real resolution.

Higurashi and Umineko take place in the same story universe as far as I'm aware, but there is no character overlap. As for Umineko, there is an entirely new cast of characters. That said, events in Umineko may shed some light on the workings of the Higurashi / Umineko universe, and it references Higurashi quite a bit.

While it is not strictly necessary, I think you would get more out of Umineko if you watched Higurashi first, even though the cast and story are entirely different. Also, if you can manage, I'd recommend reading the Visual Novels for Umineko instead of watching the anime. The anime is poorly done and ends prematurely, leaving you with far too many questions unanswered and no real resolution.