My walkthrough for this game: try everything - and I mean everything - repeatedly, at different times of day. If you're stuck somewhere make sure you have done everything with all the other characters to this point, do it again just to make sure, then go back to all the scenes of the character you want to progress with. After that go back to the other characters again because <y> might be possible now that you've reached <x>, et cetera et cetera.
It's a bit tedious, but the scenes this game provides make up for it.