The relationships of Harry Hook throughout the Descendants franchise.
Captain Hook is Harry's father, and therefore, whom he admires a lot. Harry carries a hook on his hand in order to resemble his father.
Harriet Hook is Harry's older sister.
CJ Hook is Harry's younger sister. It is presumed that they have a distant relationship as CJ is always off having adventures of her own.
Although their past 'relationship' wasn't mentioned in Descendants 2, the actors, Dove and Thomas, and director, Kenny Ortega, came up with a 'backstory' where Mal and Harry used to date. Throughout Descendants 2, their past 'relationship' could be perceived through their close interactions. Mal could be shown being somewhat comfortable around him and Harry seemed to enjoy teasing her with his hook. Harry didn't mind chewing the gum that Mal was previously chewing. However, this directly contrasts Descendants where Mal says she doesn't know what love feels like and that they don't date on the isle.
Uma is Harry's captain while he is her first mate. They consider themselves as each other's oldest friend in the Isle of the Lost. When they were kids, Uma usually ordered him around and Harry fell into the habit of following her orders. They were always up for mischief and adventure. Both of them had Accelerated Piracy: Hostage Taking and Threatening as their favorite subject in Serpent Prep. The two may have a romance each other, which is shown throughout the movie as the two are often touching, and Harry lets Uma wear his hook.
Gil and Harry are both members of Uma's pirate crew. When he was a kid, he and Harry often did Uma's bidding. The three were inseparable once, but over the years Gil drifted away from them. Gil joined Harry and Uma after Uma successfully won the Lost Revenge.
In the junior novelization of Descendants 2, Harry and Gil kissed. This scene was cut from the final version of the film. This could have indicated a romance between them.
Harry is not fond of Ben and is always ready to hook him even though he tries to every chance he gets but fails.