I just sent a PM to a friend, responding to a statement that this person and other new people have at times felt like they're intruding on a family. I thought I would share what I wrote, and add my thanks for the compliment.

"I can certainly see where you and other new people might feel a little hesitant to "break in", as it were. That troubles me, but I don't quite know how to make it easier, either. I suppose it could be treated as though you were in a new job; all the others know each other, yet you have every right to be there. Some people may reach out to you, but no one is actually obligated to. You may need to find your own way. Yes, there are some inside jokes; there are pretty well bound to be, in an established group; but you'll learn many of them in time, and become part of others, yourself."