May I ask whether or not Hazrat Abu Talib and Hazrat Khadija were part of the Ahlulbayt?

There is a specific meaning for Ahlulbayt, that is the 5 ahlul kisa. The general meaning of Ahlulbayt is family of the Prophet and that includes them. However generally speaking when we say Ahlulbayt we mean the infallible masoomeen