I find them all acceptable. I usually use "cases where" myself. I don't like "cases when" very much. Some people may find it wrong. "cases in which" is too formal for everyday conversation. They are all defining.
To me, sentence 2 sounds the best and also the most formal.
Sentence 3 might also be used, especially in more informal English, I'd say. I doubt that I would use sentence 1 myself, but I imagine some people might.