In one scene, This is Where I Leave You completely understands what a (healthy) sibling relationship is like. Let's check it out.
In the scene above Wendy (Tina Fey) and Judd (Jason Bateman) are confiding in each other about their problems. Even though the sequence is shot in a, somewhat, generic way. The performances and writing really get what it's like to have a good relationship with one of your siblings.
My brother and I never really got along but now as adults (the same way we see Wendy and Judd), I can see us having conversations like this one. If you're only seeing this scene (without having seen the whole movie), it's hard to tell which sibling is older.
To me, that's a good way to tell if two siblings really love and support each other. The conversation starts by focusing on Wendy's troubles and when she starts to cry her brother immediately uses humor to pick up her mood. The way Judd (and Jason Bateman, of course) slip humor into the conversation so naturally makes the scene feel more "real". Then the conversation switches and the focus (again, naturally) moves to Judd. Wendy becomes his support system even though she was just getting teary about her problems.
And isn't that what you generally want from a sibling relationship? Support? The way this sequence captures the shifting nature of older/younger sibling is something a lot of films miss. It's what makes the sequence so important in the realm of the film.
We really get a feeling of how close these characters are and sometimes that's rare in contemporary film.