Wedding invitation etiquette for digital card

Or you do not have to use their last name. But option 2 would be fine.

I didn't do this digitally but for the three families with kids invited I did option 2. Very few people will be finicky over the "proper" way. Unless this family is very traditional, they won't think twice about it. We had one out of our 60 something go out, so I made sure to address her envelope that way (which I absolutely hate): "Mr. & Mrs. Malelastname". Personally, there's certain ways I hate being addressed (this way lol) but it wouldn't affect my attitude towards the invite.

The family name is enough to put as the names can be added to the inside of the invite. This way it saves a lot of trouble to do more and over think other options.

What site are you using? I used WithJoy and everyone's full name can be included. You just lump parties together so one family member can RSVP for the whole group.

Is using no last name an option? At least for the address? I know they will need to use it to RSVP but unsure if your site has that option.