The church

Could the church have taken up the pact after Warren? They clearly knew about the bells and the chamber. The letter leads Bryce to the well. When he is seen again, he is traumatized, says evil lives here, calls Tom to say he’s so sorry, burns the letter and dies.

Richard clearly tells the pastor about the pact involving human sacrifice. The cannibalism happened in the church.

Also, this is a bit out there - the church be sacrificing all those dead babies for the ‘greater good’? It’s just a LOT of dead babies, which for that era might be common. Then there’s the burning of the witches, good cover for sacrifice. And no one would really suspect it’s them.