Invites! "chupin, Mickey, Titi" help

So funny story. We have certain...names...we like to call some people and those names who those certain people preffer to be adressed by. I already sent the 'save the date' invites, so now I'm working on my formal invitation's names on Excel. The thing is, there are some instructions on how to correctly address a wedding invitation, FORMAL ways of course. Titles, Mr.'s and Mrs.'s, etc. My soon to be husband asked me 'why can't we just write them how we want to? With nicknames and all?' and I've been asking myself the same question! How do/did you write the names on your invites? How formal did you go? Did you go with the "Auntie Keke" for example in a casual way, or with the "Mrs. Keke 12345 and family" formal way?