Well, it depends on the author's imagination. The Bella family might be the stars of the trapeze show, or they could be in charge of organizing the entire circus operation.
To say if the story of Keane is true is not straightforward. It might draw inspiration from real-life incidents but could also have fictional additions or alterations to make the story more captivating and coherent.
In this love game fanfic, it could start with Mabel, Dipper and Bil being transported into a magical world that is all about love. There could be different levels in the game. At the first level, they have to figure out each other's love languages. Mabel might be all about gift - giving, Dipper could value quality time, and Bil might be into acts of service. As they progress, they face challenges that test their relationships and they learn more about themselves and each other in the process.
One common theme is acceptance. The circus freaks, who are often ostracized in society, find love within the circus community where they are more accepted. For example, they might be seen as normal by their fellow performers.
A possible plot could be that an evil entity traps Mabel, Dipper and Bil in a love game. The rules are strange and they have to find true love within the game world to escape. Mabel might start by trying to set up Dipper with a character in the game, but then realizes she has feelings for him herself. Meanwhile, Bil is trying to figure out the true nature of the game and stumbles upon some secrets that could help them all.
One such book could be 'Water for Elephants' which has elements of circus life and love stories within that setting. It shows the complex relationships among the circus performers.