H.P.
ETA: I shared this with my mother, and she and I very passionately agree with you.
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I am a person who believes that family has little to nothing to do with blood and is all about choice. That said, "just like family" for one person does not make it automatically so for everyone else. A long history is different. The best friend of a family elder who's been "family" (with a handle like aunt/uncle) through generations is not the same as my sibling's best friend who's been around since junior high school. And that's not the same thing as the new love of my uncle's life, even if he thinks that this time is it.
Family photo should be relatives only.
The way that I handle these intrusions is to intentionally exclude them from certain activities and include them for others that I think are appropriate. It sounds mean, but I treat them differently. I am so very particular about my space; I won't hug someone who feels forced on me, even if I hug everyone else in the room. If I am actually having a conversation that I think is none of their business, I let them know directly that I am talking to someone else and not them.
I think that it is beyond rude for relatives to force who they consider family into intimate circles with others.