Poe’s The Fall of the House of Usher.
I did a paper my Sophomore year of HS on the whole dysfuntional relationship between them being symbolized as the crack in the wall which eventually leads to the entire castle coming down. Also, Roderick and his sister Madeline are the only remaining Ushers, since they have this weird thing going on and Roderick doesn’t continue the family line, the “House” falls.
Monica and Ross from “Friends.” 
Francie and Neeley in A Tree Grows in Brooklyn?
Scout and Jem in To Kill A Mockingbird?
The Tillermans in Dicey’s Song and Homecoming?
The Pevensies?
Not in the Ultimate 'verse.
If we’re going for any siblings, I’ll throw in Buffy and Dawn, and Dean and Sam Winchester…
Well then, how about Death and Dream?
Sound and the Fury?
Dude, you really need to read the book again-and the sequels.
Why? Once was more than enough!
I’d mention Superman and his cousin Supergirl.
Unless it was a whoosh, it was based on his comment that Chris and Cathy’s relationship never went to incest. Dude, that entire book series was ABOUT incest.
Cathy and Chris even get MARRIED later on in the series.
Although since you mentioned FITA, I would go with Cory and Carrie, the twins. They were definetly attached to one another-but not in a sexual way.
Or what about Fanny and William Price in Mansfield Park?
Joey and all his sisters on “Friends.” He defended their honors like they were his wives, and it was all played for laughs.
In the movie The Uninvited, the main characters are a brother and sister, both in their 30s, who buy a house together at the beginning; they’re very much at ease with each other, and don’t seem to be considering any other arrangement than living together. However, by the end of the film they’ve both acquired love interests, with no sign of jealousy.
I guess in your haste to post (twice) you missed Post #40 and quote it included.
The OP asked for suggestions of literature, and mentioned that they are doing it for a book club, yet I keep seeing people mention TV shows and movies. Color me confused.
Doper Mission Creep. The farther you get from the OP as the thread expands, the less likely the answer is going to actually fit all the criteria of the OP. If the thread spills over to a second page, the likelihood of perfect criteria fit drops to single digits.
Edited: Corollary to Doper Mission Creep - The above definition should not be assumed to preclude posts in the upper portion of the first page of the thread from being far afield. This is simply Doper Eagerness leading posters to reply without reading the whole OP.
I used a broad definition of fiction. 
Well, for book club purposes, we’re specifically talking about brother-sister relationships. But the thread may go wherever zeitgeist takes it.
:smack:
Sorry 'bout that.
But I think the Dollanganger twins definitely fit the definition the OP stated. As well as Chris’s and Cathy’s devotion to said twins.
Well, the Dollanganger saga was a family tradition: There mother Corrine married the man she thought was her half-uncle, son of her father’s brother and his young wife. Of course, it was later revealed that they were half-siblings, Christopher having been fathered by Malcolm, Corrine’s father.
Yes, I agree there. The mistake I made is thinking I remembered the details of some trash I read over 30 years ago and vomited back up at the time.
Um…what, exactly, is a half-uncle? 
Unless you’re using it to mean “half-brother of one’s parent,” that phrase seems pointless to me.