Envelope address mother and son

I would just do their names, like "Jane Smith and John Smith."

View Quoted Comment Ohh ok I thought that Jane and John Smith was fine. But maybe is because this would be for married couples right?

View Quoted Comment Yeah, that reads more coupley to me. Technically, if the nephew is an adult, he should get his own invite but you said that you aren't being very formal.

If the nephew is an adult he gets his own invitation. If a minor his name goes on the second line.

I have this situation as well where my cousin still lives with his mother. I am putting just their first names and their last name. To me, it’s just an envelope and as long as it has the names of both people on it, it really doesn’t matter. They would not be offended that it was addressed that way.

Is the son 18+? If so, he should get his own invitation. If not, just address it to both of them by name. Ms. Aunt First and Last and Mr. Cousin First and Last, or however you’re formatting your names.

I put children’s name on the second line - if they had the same last name as their parents, I did not include the last name.
I know that etiquette is that every adult in the same house should receive their own invite - however my family has multiple adults living in the same homes & sending to every adult would be perceived as overkill (I would get comments). They will only keep 1x invite & put it on their refrigerator. So I sent 1x invite, w/ multiple RSVP cards per adult.

I'd just put their first and last names.