So, it's been asked on the discussion tab of the store page for Haunting of Harrowstone, and asked elsewhere, but never answered.
Is the Changeling's ability bonuses a typo? It looks both in the description and in the statblock for a sample changeling Witch that it should be +2 Int rather than +2 Wis. I don't have the module in specific, so I can't check if it's just a PFSRD typo.
Would be nice to get some confirmation on this, as it wasn't ever answered in the discussion.