I don't really know how it works but according to a lot of other people here it doesn't work unless you are in the same region. This isn't the only person here saying they can't use it because they don't live near their family.

They're doing IP location checks, and they're doing them badly (there's not really a way to do them well). It's not working for me with people in the same town, and other people are reporting it's randomly working or not working with locations in the same neighborhood.

I get a big red banner saying sorry, according to your usage patterns you are not in the same family.