so confused with addressing

OK. so...lol

I have no inside envelopes.
Just an outside envelope and obviously the response envelope.

Am I suppossed to treat the outter envelope as if it was an inner?

Like....heres 2 questions.

single Man but has GF that he does not live with
outside envelope: Mr. Michael Smith & Guest ?

also

Married cousin with 4 kids
outside envelope: Mr. & Mrs. John Smith & Family
or list the kids names and how?

also

Married cousin with baby (shes like 8 months)
do i address & Family or list babys name

oh my god...im so confused!!

Ahhhhh addressing envelopes~fun fun fun
I would do this:
If you know the single guy's gf's name and if they've been together for a while, add her name.
**I did an invitation like that for a single guy, I put 'and guest' & the gf got offended**
Married cousin with kids, I'd put 'and family' (if the kids are invited, of course)
Married cousin with baby- I'd put 'and family'
HTH