In the movie, Charlotte and Harry also let Carrie Bradshaw - portrayed by Sarah Jessica Parker - and husband Big move in with them when they lose a huge amount of cash in the recession.
Big - played by Chris Noth - eventually travels to the Middle East to try and recover their fortune.
Cynthia Nixon's character, Miranda Hobbs, makes a life-changing decision when she leaves her career as a lawyer after being sued for malpractice and opens a restaurant with husband Steve.
It is also thought Carrie's gay best friend Stanford Blatch will marry camp wedding planner Anthony Marentino, with Liza Minnelli making a cameo singing at their reception.
A source said: "All signs point to a gay union between Stanford and Anthony Marentino, who's required to wear a black tuxedo in the scene. Slated as the entertainment: Liza Minnelli."
The highly-anticipated movie is due out next May.