House Arrest

The film is told through the perspective of Grover and TJ through the literary device known as a frame story. The two are shown in silhouette form watching the original film, House Arrest, in a style nearly identical to that of Mystery Science Theater 3000.
Grover interrupts the film to fast-forward to his scenes, but TJ protest prompts Grover to share his backstory. showing the Beindorfs, Janet (Jamie Lee Curtis), Ned (Kevin Pollak), Gregory whose nicknamed "Grover" (Kyle Howard), and Stacy (Amy Sakasitz), a supposedly happy family living a typical family life in the suburbs of Defiance, Ohio. It is revealed that Janet and Ned are not happy and in fact separating although they tell their children it is not a divorce. Grover and Stacy first try to recreate their parents' honeymoon in the basement of their house but this fails to bring any happiness into their relationship. The children then leave the basement telling their parents they must get another surprise for them upstairs. They go up, close the door, and nail it shut. They vow to keep it shut until their parents work out their problems.
The next day, Grover tells his best friend Matt Finley (Mooky Arizona) what he has done and T.J. Krupp (Russel Harper), the wealthy local bully, overhears the conversation. Matt goes over to the Beindorfs' house to look at the children's work and is impressed. T.J. shows up to have a look and actually installs a newer, more secure door to keep the parents trapped. He and Matt then leave to collect their parents and bring them to the Beindorfs' house to lock them up as well. Matt's father Vic (Wallace Shawn) never keeps a wife for more than two years and T.J.'s father Donald (Christopher McDonald) does not treat his wife Gwenna (Sheila McCarthy) well. Matt also brings his bulldog Cosmo and his two younger brothers, Teddy and Jimmy (who come armed with sleeping bags) and T.J. brings Spot, his pet boa constrictor. When Grover asks what is going on in response to his friends setting up camp at his house, T.J. replies with "Our parents could be down there for months!"
Janet and Ned almost talk Grover into letting them all out but T.J.'s father, Donald (who's an attorney), threatens him with legal action. Grover finds out that his dream girl, Brooke Figler (Jennifer Love Hewitt), is also having parental problems: her mother Cindy (Jennifer Tilly) acts like a teenager, going so far as to trying to hang out with Brooke's friends. Grover invites her to lock up Cindy with the rest of the parents. The children lock up all of their parents and begin to help them solve their problems. They try to find a way out of the basement while getting along and seeing what each of their problems are. The children also work out their differences with each other above. They eventually give in and give up to the police and their parents are set free. It is revealed at the end that Grover's parents reconciled and took a second honeymoon to Hawaii. Matt's parents' wedding lasted past the two-year mark and they are expecting another child. T.J.'s parents got divorced though his mom later went back to law school and they opened up a law firm together. Brooke's mother started dating other men instead of intruding on Brooke's dates. Also, Grover and Brooke became boyfriend and girlfriend and she passionately kisses him in front of their classmates at school for a very long time, causing a slightly awkward moment for the bystanders. However, he concluded if their parents ever try to get divorced again he might think of locking them in the attic. In the final scene of the film, Matt Finley, Donald Krupp, Ned, Janet and Stacy join Grover and TJ to re-watch the film in the cinema. As the film fades to black, TJ reminds Grover that he still doesn't do well in crowds.

Question: Who prompts Grover to share his backstory?
Answer: T3