Injustice always feels insane -situations in which we feel wronged can be crazymaking, for sure.
But what can also be insane is shooting ourselves in the foot on the principle of the thing, to teach a lesson, etc.
If getting quick possession is the most important thing, take the steps to get that.
If saving money is the most important thing, take the steps to do that.
If proving a point/standing for justice is the most important, that's a different step again.
Any of these goals is legitimate. Only your inlaws know what's most important to them. They should do the steps that align with their primary goal/interest.
I think several of us have been under the impression that quick possession of an intact place is the primary goal here, hence the suggestions.
Where I live, a person can't be kicked out just because a place's ownership is transferred. The laws here consider *that* unjust, because of the impact on the person residing. So, justice, ethics, etc, are complex matters, with lots of subjectivity. Because this is so, and because laws can reflect such, lots of landlords negotiate, offer a small payout in order to achieve their preference, etc. One of the best tools we have in our region is a form called a Mutual Agreement to End Tenancy. It encourages and empowers landlords and tenants to work out a compromise, and I've found it a very effective tool as a landlord, manager, and tenant.