This presupposes "Aunt Sally" or "Uncle Bob" are using Google+. I'm a fan of Google+, but I would contend that, in general, they are not. (They're using Facebook).
As an aside, I think most typical users of social networks have been conditioned to post to one of two groups: public or friends only. Facebook doesn't have "circles" but it has the capability to allow selective posting to default groups or ones a user chooses. I don't think most bother, there or anywhere really.
In general, perhaps not. But my mom is one of the least technically-savvy people I know (superceded by my grandmother), and she uses it. Mainly because she for some reason figured it was more convenient to share posts with a "Family" circle than it was to write e-mails cc'ed to all her kids. And my mom never did get around to Facebook.
Anecdote, I know... but hey, it's an existence proof, at least.
You have a cool mom. My entire family, extended, blended, and otherwise is on facebook. I try to get people to look at & use Plus but there's just not a lot of interest.
As an aside, I think most typical users of social networks have been conditioned to post to one of two groups: public or friends only. Facebook doesn't have "circles" but it has the capability to allow selective posting to default groups or ones a user chooses. I don't think most bother, there or anywhere really.