Yes they do mix houses in the classes, but there's a huge social pressure for them to not make friends in different houses. Also I think Ginny should be in Slytherin - so non-evil Slyth, and add in an arc about what happens if someone "Breaks" tradition that isn't just throwaway background information (Ron dealing with his little sister being in the "Dark Wizards" House, and forcing him to rethink things)
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Yes they do mix houses in the classes, but there's a huge social pressure for them to not make friends in different houses. Also I think Ginny should be in Slytherin - so non-evil Slyth, and add in an arc about what happens if someone "Breaks" tradition that isn't just throwaway background information (Ron dealing with his little sister being in the "Dark Wizards" House, and forcing him to rethink things)