Here is a guide copy and pasted from the 360 Achievement. Credit to Agent CH
Ron - You have him already.
George - 2-1 - Dig outside the house at the start, at the far right.
Arthur - 2-1 - Use Dark Magic in Borgin & Burkes.
Molly - The Great Hall (Hogwarts) - Use Reducto on one of the chrome objects.
Ginny - Defense Against the Dark Arts Classroom (Hogwarts) - Use Dark Magic.
Percy - The big outdoor area (Hogwarts) - Pluck the carrots out of the ground with Wingardium Leviosa.
Fred - Transfiguration Class side room (Hogwarts) - Use Reducto in the Transfiguration Classroom to get here. The token is behind the chalkboard.