I wouldn’t mention the sister at all. I’d go as far as cutting Obi-Wan. The whole scenes feels… strange. In ESB he was always lurking around, telling people things through the force. He only shows up to help Yoda convince Luke not to leave. But in ROTJ he just shows up and has a full on conversation with Luke. Sort of takes away from his scarifce- Ben could have tought Luke as a ghost without Yoda. And then there’s the conversation itself, home to certain point of view, ghost on a log, and the sister reveal. I think it would be much more powerful if when Yoda dies Luke truly is alone.
Now I’d already intended to cut the sister aspect from my edit, but cutting Obi-Wan from that scene altogether is an idea I hadn’t considered, and definitely worth looking into.