This. Your family doesn't use HN or reddit, but you do. You can use GNU Social the same way, and maybe it will attract your family to it over time as well.
Apples and oranges. I use HN and Reddit because those have communities centered around certain interests (tech news here on HN for instance). So I come here to chat with people about tech topics. The design of the forum facilitates this, by people posting links to articles and then us discussing them.
Places like Facebook are full of random people, generally who you know but for a brand-new social network would be just a bunch of unknown randoms. I'm sorry, I have no interest in trying to strike up a conversation with some random person who could be anywhere on the planet. There needs to be some kind of commonality, some reason to interact. On Reddit I can go to a subreddit centered on a certain esoteric topic and chat with people about that. On OKCupid I can try to chat up women who live near me and have interesting profiles and go out on dates with them. On GNU Social, what am I going to do there? I have no idea.
The nature of gnu social and ostatus is that the users of it, by the nature of it being niche, are technical. The major feed usually contains almost exclusively developers and FOSS activists talking about coding or software freedom.
That is the commonality right now on ostatus, and new communities can join it any time and form new centers of commonality.
Sure it doesn't replace existing communities or networks. But it's creating new ones right now.
You just have to believe in it!