Absolutely! Just remember to count them when RSVP-ing.
As long as you are there, we don't care! (But remember, the wedding will be heavily photographed)
As long as you RSVP for the appropriate number of guests, go for it! However, if you do not, please bring an extra chair and meal for your friend.
Please see the "Travel" tab for more info. Steinhatchee is a scalloping community and (thankfully) the wedding is during the off season, so hotels and cabins should not be booked up.