Jessica was not willing, and deep down, neither was Hank. So only by ameliorating his relationship with Liberty could they get Zachary to spare them.
If he knew earlier that Serenity was Mr. York’s wife, even if he had to drag it out, he would have done his best to delay divorcing Liberty. Then Serenity would not have allowed Zachary to force him into a corner for her sister.
Unfortunately, these were all thoughts in hindsight.
At the time, he had suspected that Zachary was “the” Zachary York