The hard part of it is that nobody has told me they have any difficulties with the plot at all. Nope, everything hinges on expanding the characters and their motivations. Everybody knows exactly what happens, but they don't know why . Right now, I have a 115-page screenplay, so I can't add too much more, or it'll be way over readable limits. Especially for a comedy.
Nobody gets excited over a comedy that's more than two hours long.
So I have to make some cuts, in order to insert a few revelatory scenes in which to expand upon each character. Luckily, I don't think it's going to take long stretches of movie time to get the point across. I can re-work some existing scenes to shine a little more light on what these characters are thinking. Even a change of setting will help now and again. It's just a matter of knowing where to dive in, cut, add, and leave.