T.K.
all that truly matters is that everyone is together, safe, sound, and healthy. suprise would've been nice, but too hard to keep when you have people in on it.
Look at the positive that everyone will know. That allows people to plan accordingly, get your rooms ready, shop for extra groceries, rsvp for other parties etc. Suprises are nice, but are sometimes inconvenient for the suprisee.
I would send out a great big announcement email - hey everybody, great news, thanks to so and so we will be able to make it for Christmas this year afterall. Can't wait to see you all. Please ship gifts, as the airlines are charging $30 a bag. We wont have room to take gifts home on the plane. Get the mistletoe ready, this is going to be a great Chrsitmas.