What I mean is, the rules for that trait specifically say it only applies when defending a member of your family--and nothing says you can declare a person or group "family" in order to benefit from it.
Now, if you had a regular PFS group, and all the players agreed on a common backstory that included each PC being related to each other, then it would kinda', maybe fly--but honestly I wouldn't be surprised if this trait is specifically banned from PFS. They've swung the banhammer on much more innocuous things.