Okay, come to think of it, only one of my five novels actually didn't have family in it. In fact, my first novel completely revolved around family--or the lack thereof.
So now I've debunked my own theory that I don't write about families.
Still, I certainly haven't written such a large family before, and this one extends in several gnarly branches, too. There are a lot of female relatives to boot, which is something I'm having to flex the ol' writer's imagination on. I don't have any sisters and never had many close female friends growing up--the closest thing to sisterly camaraderie I've ever enjoyed was with my 2 cousins growing up, and we only saw each other once a year or so.
I dunno. Seems like a lot of the protagonists in urban fantasy (which the new WIP is) don't have strong family bonds. I guess it's a lot easier to be in mortal peril and save the world when you don't have to call Mom every Sunday, right? Or is it something else?