Nobody signed a contract with these people promising to let them live there forever. They were rentors, and if they didn't understand that they could be asked to leave at any time by the true owners of the property, that's their fault. And if they were so concerned about their ability to continue living there indefinitely, maybe they should have worked harder to ensure their position? Maybe they should have striven to provide more economic value, so they could have purchased this apparently extremely important good?
These people have no excuse. They knew the rules. The rules were clear to everyone. They were happy as long as they got what they wanted. Now the situation no longer favours them, they want the rules to be changed - so that they get everything exactly how they want it.