The article lists the members who are suing and it appears Ron Howard and Henry Winkler are not involved.
Prolific directors have a habit of not wanting to PO a major network. Both probably think that having a major network mad at them could cost more in the future then they would ever get from this lawsuit.
The show was originally on ABC but CBS could own the rights to it now.
They might've had residuals and merchandising profits written into their contracts.