I am not well versed in property rights laws, but this seems messed up. Sure it is an anomaly of a situation, but why not do it 60 years ago when you expressed interest? They probably could not until recent changes.
Couldn't find any reading about their processes in the courts, even though this battle has been going on for quite some time.
Other links: http://wideawakenews.com/2015/09/04/family-near-area-51-fights-back-after-government-tries-to-confiscate-property/