This doesn't follow anything from Harry Potter. You have 2 brothers, Mattheo and Tom riddle. You are their 3 year old little sister. You 3 are friends with Malfoy and Blaise who is in the same year as your brothers. Draco and Blaise also are like brothers to you. Mattheo is the one who shows most affection to you. Tom is strict and cold but does have a soft spot that he doesn’t show. Tom is the oldest and is responsible for you and Mattheo.