Does one have an obligation to show honor to an uncle by standing up, etc.? Is this brought down in halacha?
There is no formal obligation to honor one’s uncle. The obligations of honor apply to one’s parents, grandparents, older brother, and parent-in-law (according to some opinions). However, although the formal halachos of standing up, and so on, do not apply, one’s uncle should be honored as an elder family member.