my idea for the ending

it was an ok movie but just stopped rather than ending. here is what I would have done:

you'd need to establish that Adam is gradually being overtaken by Zachary. the setup would be as per the alternate ending in which the church scene has happened, the wife has been trapped in the dark room and Adam has created the gas leak.

DeNiro arrives, confronts the Adam (addressing him as Zachary) and Adam says something which makes DeNiro realise he is intending to kill the wife. DeNiro finds the wife passed out in the cellar and starts to carry her out. He is attacked by Adam who DeNiro knocks unconscious.

DeNiro carries the wife out of the house and onto the lawn away from the house. he then returns to the cellar and revives Zachary/Adam. he tells him they can go away together but Zachary does not believe DeNiro loves him, says "you shouldn't have rescued her first" and fatally stabs him.

Now dying, DeNiro realises the kid is pure evil. Cut to outside and the husband arrives back to find his wife alive (but only just in the house). she tells him Adam is in the house. he makes his way towards the house.

cut back to the cellar. DeNiro knows the boy can't live. He takes hold of him so he can't escape, grabs a nearby tyre wrench and starts hitting it on the concrete floor. a spark ignites the escaping gas, blowing up the whole house and throwing the husband backwards. he and his wife survive and the film fades out as they stand viewing the wreckage of the house.