Envelope Addressing

OK.....I broke out the etiqutte book, but couldn't find how to word this......
How do you address an envelope for a gay couple?
They are 'married' (not officially, however, bc they live in NY), but I have no idea how to word this?
And what is the salutation? Mrs.? Ms.? Miss?
Do I just list their names? Please help! TIA

I've had this situation and I've always done it:

Mr. Joe Smith
Mr. John Brown

Or

Ms. Jane Doe
Ms. Sally Jones


On the inner envelope I would just put Joe & John or Jane & Sally to indicate you are inviting them as a couple.