I would not urge you and Julie to see humor where you just don't find it. However when I speak of humor, I don't mean laugh out loud mirth. I mean a wry type of humor where the because the characters are at their worst, so bad and at such cross purposes that it becomes a bit funny to me.

I think Jane Austen carefully drew this whole scene to lampoon (for lack of a better word) the bad behavior and perhaps the idea of selfishness altogether.

It's sad that the innocent suffer from the selfishness of the others. But suffering from others' selfishness seems to be par for the course for Fanny, and poor Mr. Rushworth is destined to suffer more as things are shaping up.

I am particularly struck by Maria and Julia on this read. I'm not pointing out humor here, just studying their characters.
Maria “There could be no harm in her liking an agreeable man— everybody knew her situation—Mr. Crawford must take care of himself.”

Julia The politeness which she had been brought up to practise as a duty made it impossible for her to escape; while the want of that higher species of self–command, that just consideration of others, that knowledge of her own heart, that principle of right, which had not formed any essential part of her education, made her miserable under it.

When they are passing out parts for the play, Mr. Crawford slights Julia, choosing Maria to be Agatha, but then tries to butter Julia back up, by insisting she take the part of Amelia.
She looked suspiciously at her sister; Maria’s countenance was to decide it: if she were vexed and alarmed—but Maria looked all serenity and satisfaction, and Julia well knew that on this ground Maria could not be happy but at her expense.

I think something is very wrong with these sisters. I don't mean to minimize the creepiness of Henry Crawford here, but just point out how there must be some underlying lack of true caring for each other as sisters, for Henry to drive such a wedge between them. My compare-o-meter can't help but think of Elinor and Marianne and the fact that they would hurt each other in this way.

My point in all this I guess is that we need to keep a close eye on these Crawfords and their bad influence on the MP family, but also a close eye on the MP family and the clues we've been given in their inner thoughts, that maybe despite outer politeness, underneath may not be innate goodness.

I agree that Box Hill is painful to read, because I hate to see the heroine, Emma be so mean.