They might be able to ban sterling, but they can’t ban everyone related to him. Guilt by association would never in a million years stand up in court.
Under the league rules the NBA has to approve the sale or transfer of a team to a new owner. Since transferring ownership to Sterling's wife or to his kids would be an obvious ploy to sidestep the league's sanctioning of him then there is no way the owners would allow it and no way a court would overrule them.