Ok. Before anyone says anything, I know how invitations should be addressed. Mr. & Mrs. John Doe. I'm pretty sure of the answer but I'm still going to ask anyway. I'm coming up with my list of addresses and I just wrote down my father-in-laws. The problem is that it seems weird writing his first name down (as that is also my fiance's first name). He has always gone my his middle name. Would it be completely wrong to use his middle name on the invite?