Invitation Mailing Time ...inner envelope question??

I'm finally sending out my invites today. i'm home sick, so now is the perfect time... I have a guestion about the inner envelope...
Am I supposed to write the first & last names of the people invited on the inner envelope or is just the first names ok....
Like for the address label i have 'mr & mrs. john smith'.... for the inner envelope would i put -- 'John & Susan' or ' John and Susan Smith'

I definitely need to put names on the inner envelopes because some of our friends have children and I want to make sure they see their kids names are NOT on the invite, meaning they are NOT invited

I figured the inner envelope would be addressed more casually than the outer...or am i wrong? am i correct in using the first names at all?

TIA!!

if the outer says Mrs. & Mrs. John Smith the inner would say Mr. & Mrs. Smith

WHen I spoke with 'my lady' she said you could do it either way...Mr. and Mrs. Smith or Jane and Joe.

If you are writing the first names, you do not have to write the last names. I'm doing Mr. and Mrs. Smith to make them a little more formal.

Now this may sound TOTALLY stupid...but the inner envelope...what is it?? lol Is it the RSVP envelope, or is there some other envolpe that everything should go in..??? Sorry so dumb...but I'm soo confused!

Oooo....I'm making pocket folds...so I don't need them. LOL. Thanks sooo much!!!