addressing invites and guests

Ok I have a question. I only have an outer envelope(no inner), so if I am inviting my friend with her long time bf and I want to include his name instead of 'and guest' do I need to put his last name too???

Would it be:

Ms. Jane Smith and John

Ms. Jane Smith and John Brown

Ms. Jane Smith and Mr. John Brown

????????????????????

and if it is the third one...do their names go next to or under one another???

I know some etiquette says to send a whole another invite to the guest if you know them but im not gonna do that.

Any advice???

TIA!!!

Ms. Jane Smith and Mr. John Brown is the way I'm doing it.

When FH and I first started dating, my cousin had a sweet 16 and my aunt addressed the invite to Allison and Tom (my last name) because they didn't know his. He was like well guess I'm part of the family now whether I wanna be or not! He got all touchy that they were moving our relationship along too fast.