I have 2 probably common but tricky situations when it comes to addressing envelopes.
1. My future FIL has always gone by his middle name (he has the same first name as his late father). When addressing his should I put his full first/middle/last name or maybe first initial and full middle/last name?
2. My future MIL goes only by a nickname, and is quick to correct anyone who calls/introduces her otherwise. If I put her legal first name I will probably hear about it years after the wedding but she's also educated and probably knows the whole etiquette thing, and I might hear about that instead if I don't put her legal name. If I had to choose which one I'd rather hear her talk about, it'd probably be the etiquette.
I was planning on using only 1 envelope but now I think I need 2 (especially for them) so I can feel good about properly address the outer envelopes but they can keep the inner one without the postage and "wrong" names.
Re: Nickname vs. Legal First Name on envelopes
But, then again, I know this because I know them very well. I would ask your FI, and if he's clueless, just ask them.
If the nickname is a more casual, group of friends type nickname, I'd put their actual name. (e.g. I call one of my friends Scotty, but he generally goes by Scott, so his invite was addressed to Mr. Scott Jones.)
EDT: Correcting name we put on invite. My brain is already on a long weekend.
But don't assume you know. I go by a diminutive that most people associate with a very common name. If they were to guess at my legal name without checking, they are almost guaranteed to be wrong.
When I entered the working world, it was easier to just use my legal name, rather than the one my Mom insisted I use. Explaining it made no sense to anyone (unless they knew my Mom). There was a big controversy when I was married. Which name should I have printed on my invitation? I used my legal name. I sign my legal name on all important legal papers, checks, and anything work related. I sign the other name on letters to family and close friends.
I was SO HAPPY to become Mrs. John Doe! Much easier! Jane Susan Mary (Smith) Doe.
From what I remember of my mother, she goes only by her middle name. The only people that address her by her first name are government officials. If she were to receive an invitation addressed to her first name, she would be majorly annoyed because she simply does not go by that.
I would have FI ask his mom what she'd prefer to have the invitation, program book, and place cards reflect and leave it at that. There's nothing harmful in asking. He can even stress that you want to be "proper" but it's important that you identify her by the name she wants to go by.
DH goes by a shortened name -- Matt instead of Matthew, as an example. He is a junior and FUCKING HATES his full name, because it's his assholes father's. If he gets something addressed to 'Matthew' and it's not from the government or his employer, he will chuck it out -- including wedding invitations.
His rationale is that anyone who knows him knows he goes by 'Matt' and if they don't, he's not interested in attending their event.
I have dug things out of the trash to fill out RSVP cards.