"On top of that, Betelgeuse is shown to be a bad person throughout the movies". That isn't true. The truth is more complex than being inherently "bad" or "good" which is what makes Beetlejuice fun. In both movies his help was desperately needed, and in both movies he only helped the "good" people who deserved it. Then wrap that around the fact he only helps when there is something in it for him. He isn't wholly good or bad. He did save her daughter's life. I would like to see them become quirky friends with quirky respect in their own way without contractual demands. That would be a good way to have character growth without being weird about it.