Complex sentence: In the third series, the family sell their house and move to a rather run down hotel (inherited from Aunt Agatha), Harry was studying for his GCSE's back at his old school and so wasn't featured much in this series.
Split into simpler sentences: In the third series, the family sell their house and move to a rather run down hotel, inherited from Aunt Agatha. Harry is studying for his GCSEs back at his old school and so is not featured much in this series.