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Well, an email specifically to the people who received save the dates would be far preferable to Facebook. And if they have Facebook, then they should have an email address. Or call them.
Or, I'm sure if they have questions and actually need the hotel information, they'll call you. Honestly, I've never needed hotel information that far in advance. So really, any inserts you're putting into your invitation is sufficient notice for that sort of thing, particularly if you have a block reserved. The save the date is literally just that...and FYI to just keep that date reserved in the back of your mind when making other plans and maybe start pricing flights if you have to fly. Other than that, it's really not that crucial for people to make reservations and know this information that far in advance.