It seems to me, based solely on what I read in the linked articles, that Nicklaus should have engaged better legal representatives to negotiate the deal on his behalf.
I’m only speculating here, so I could well be mistaken, but when the entire family earns its living off one man, that could have played a role in encouraging JN to enter into this arrangement in the first place. It’s not unreasonable to think that the children had an incentive to monetize their father’s brand and likeness. I’m sure JN himself was not disinterested in the idea of monetizing the business and taking a significant upfront payment. It wouldn’t be the first time, and it certainly would not be the last time (see Gary Player and family, for example).
Because I’ve lost respect for Nicklaus over the past few years, I also find it somewhat ironic (and I’ll admit, not entirely without humor) that someone who believes in unfettered capitalism and is worried about being able to “continue to pursue the American Dream and not evolve into a socialist America” (his own words from 2018) is upset that he felt disrespected, controlled, and owned by his business partner. That’s called employment, Jack. Welcome to capitalism.