The Dullahan were those who tried to possess the empty husks of their old bodies. But they were never whole. The only thing holding the separated bodies together was their resilient spirits.
The Hagwarders (yes, based on those ones) were the spirits who sewn themselves new bodies. They protected the town as best they could, for not all spirits were good.
Of the spirits who never passed on, many held great contempt and continuously tried to seek vengeance on their enemies beyond the grave. The Hagwarders founded the town of All Hallows and gave shelter to other lost spirits, defending against those with these vengeful desires.