The long-developing reboot / spinoff / sequel / whatever is back in action, with The Fate of the Furious director F. Gary Gray in talks to take the reigns of the next chapter in the MiB saga.
The filmmaker most recently directed The Fate of the Furious, which, though largely disappointing, still made serious bank at the worldwide box office.
To answer your first question: No, Will Smith and Tommy Lee Jones are not returning.
Like previous installments, the new film will center on the eponymous top-secret underground agency, which monitors and polices extraterrestrials living on earth.