M.C.
I would. post something to the family page addressing everyone. I would not offer assistance, that will definitely bring requests to stay at you house. I would price some close hotels, block of rooms,etc. then post something like...
For those planning on attending the summer reunion on Xxx, we will not be able to host overnight guests. Here is a list of nearby hotels and prices. If everyone books at the same place we may get a better rate overall. Thanks for understanding. We can't wait to see everyone!