For anything you want to know about Harry Potter lore, check out Harry Potter wiki.
There is interesting discussion on this website about many aspects of this movie: symbols, setting, tone. It is written based on the book, but I think the information is appropriate for the movie as well.
Sirius Black (Gary Oldman) is established as an outsider from the beginning. He is a “killer on the loose” and everyone is afraid of him. He is also an animagus, which makes him a bit of an outsider because few people can turn into animals. And he turns into a dog that looks like a mutt. He is not a breed of dog. He is simply a dog that does not belong to any one breed.
Professor Lupin is also a misfit. Because he is a werewolf, he literally has to estrange himself from other people every month. After we know he is a werewolf, he constantly refers to himself as “someone like me”. He cannot even refer to himself in actual terms because he is so different that others, especially parents, would not understand. Also, when he takes sides with Sirius in the Shrieking Shack, he is estranged from Harry, Ron, and Hermione. However, when they learn the true story, all five of these misfits join together.
The Weasley twins (Oliver Phelps and James Phelps) are also misfits. They are the trouble-makers who are constantly looking for places to cause chaos. That is why they give Harry the Marauder’s Map. They want him to go and do whatever he wants. Also, throughout the movie, we only see them together. They are literally separated from other students, whether chosen or not.
Professor Severus Snape (Alan Rickman) is also an outsider. He is constantly under suspicion throughout the movies because he was a death-eater. Most people do not trust him, including Harry. However, Lupin does not even trust him with the map. He takes it immediately saying, “I shall investigate any hidden qualities it may possess.” He would rather look at it himself rather then turn it over to Snape.
Peter Pettigrew (Timothy Spall) was also an outsider. He was “always trailing after Sirius Black”. He was an outsider as a student and even as a death-eater. He was so afraid of Voldemort that he turned the Potter’s location in to him. He was a misfit who turned to James, Sirius, and Lupin for a sense of belonging, for friendship, but fear of his master overrules even friendship.
Even to a point, Buckbeak, the hippogriff, is an outsider. Because he attacked Draco Malfoy (Tom Felton), he is condemned to death. Although Buckbeak is not killed, he is a fugitive now. Because the Ministry of Magic thinks he should be killed, he needs to stay in hiding to survive.
There are lots of misfits throughout this series. One of the underlying themes is banning together to overcome anything. Therefore, these misfits team up to accomplish whatever challenge they may face.
Thanks for reading! Come back next week!