During the gameplay reveal trailer, Avalanche introduced their "companion" mechanic. Throughout the game, you can meet and befriend other students who will help you, request your help with side quests, and teach you magic you might not be able to learn in other ways.
Amit Thakkar
House: Ravenclaw
Confirmed on November 18, 2022, Amit is an aspiring historian. He reads a lot and has one of the best telescopes you could ask for in 1890.
Everett Clopton
House: Ravenclaw
This is one of two companions who were revealed on January 11, 2023 as part of the voice-over actor acknowledgements that accompanied the release of the Simon Pegg video. He is voiced by Luke Youngblood. No further details are available at this time.
Garreth Weasley
House: Gryffindor
Throughout the gameplay reveal trailer, there are several views of a red-haired Gryffindor student speaking with the main character in a cutscene and dueling Sabastian Sallow in the DADA classroom. While his name was not revealed during that video, his name was finally included in the Hogwarts Legacy art book. He certainly fits the bill of the "Weasley or two"--the second Weasley presumed to be the deputy-headmistress whose last name I can't remember just now. One of the conversations a user can overhear while passing through Central Hall indicates that Garreth is the nephew of deputy-headmistress Weasley.
Garreth is one of several students who are members of the Crossed Wands Dueling Club.
Mahendra "Peel" Pehlwaan
House: Ravenclaw
This is one of two companions who were revealed on January 11, 2023 as part of the voice-over actor acknowledgements that accompanied the release of the Simon Pegg video. He is voiced by Adam O'Connor. No further details are available at this time.
Natsai "Natty" Onai
House: Gryffindor
Notable for her bravery, it appears based on the gameplay reveal trailer that you meet Onai in your first Charms class. She also appears in the background of many scenes (including during potions class), makes an appearance in the original announce trailer calming a graphorn, and appeared in the extended version of the "Saving Highwing" mission cutscene which was released during the AutoDesk event on August 3rd, 2022.
In their social media posts of October 5th, 2022, it was revealed that Natty is originally from Matableland in Africa, that she attended the world's largest school of wizarding, and then transferred to Hogwarts in Scotland after her mother was given the job of divinations professor.
Poppy Sweeting
House: Huffelpuff
If there was one companion to take the title of "magizoologist", it would be Poppy Sweeting. She appears in multiple scenes featuring beasts including a run-in with a dragon. In a tweet posted on the official Hogwarts Legacy account on October 7th, 2022, a caption revealed that Poppy, "has a particular aversion to poachers and those who work for them".
Sabastian Sallow
House: Slytherin
Rumors persist that one or more members of the Sallow family suffer from a curse--though it is unclear at this point what type of curse that could be. Sabastian's appearances in the gameplay reveal trailer were limited to dueling the main character in DADA class, getting into trouble for sneaking into the restricted section, and staring daggers at the main character when he gets an inordinate amount of attention from their herbology teacher.
In subsequent social media posts (including in a tweet on October 3rd, 2022), it was confirmed that Sabastian's sister Anne Sallow has an inhereted and debilitating curse and that he is so desperate to find a cure that he has begun to dabble in the dark arts. At Gamescom on August 23, 2022, the developers released a new game trailer called the Sabastian Dark Arts trailer in which we see a small portion of the side quest involving his search for a cure for Anne. In that trailer it was revealed that as payment for passage beyond a magically locked door either the main character must cast the spell Crucio on Sebastian or Sebastian must cast the same on the main character and he leaves the choice up to the player.