Well, I finally did it.
I sent facebook friend requests to some of my wife's relatives and one of her friends. So far, no reaction. Of the 4 invites I sent, I'm certain that 2 of them have logged into facebook and done other stuff since, but I've had no reaction. Not even a message saying "who are you?"
I guess I'll just have to wait a while and see if anything happens. After being so nervous about sending them, it seems like a bit of an anti-climax getting no response at all!
Maybe I should send a request to my father-in-law too. LOL.