Wider range of movement is pretty much what I'd call hypermobile. Caused by slacker tendons, I believe. It runs in my family too.
My son can do things that look really scary! So can my sister.

Yes, the youngest is Oswin, and she's made good friends with the other two youngest. All three of them are in the longsword team as well.

BTW Oswin is a big fan of the Erin Hunter books - are those ones you read?