Save the date address

I think either could work it would just depend on 1, how formal you want to be and 2, your relationship with them, for some of my parents friends we are putting the more formal and for our friends we are doing more casual

We just did their first name as all of our guests are very close to us. The handful that we are not close to (parents friends) we just did first and last name!

Formal as to putting the actual guests name on the invites. Some prefer the first way or going by family if they know they want to make simple.

Our save the dates themselves were very casual so we kept the labels casual to! First and last names but no Mr. Mrs. Ms....

Oops. I totally did casual and didn’t even think about it lol. No one seemed to mind haha

Traditional wedding etiquette would say to do full formal address, on anything that gets mailed out. But it's up to your discretion with younger friends/family

I plan on putting Mr. and Mrs./Ms./Miss for all the guests (of course no kids will be attending). As long as you don't have anybody that identifies as a They/Them or what have you - you should be fine going that route. If you do though just be mindful

For the older couples we did Mr & Mrs. For everyone else we just did their names.