I was thinking something like:
Ron Weasly had a twin and she was in Slytherin
Draco Malfoy had a twin and she was in Gryffindor
Pick which one and than let me know if you want to do Ron/Draco's perspective or the twin's perspective. For Draco's twin, I was thinking the name Emma and for Ron's twin, I was thinking the name Mia.