Horror.com Forums - Talk about horror. - Searching for a Movie from late 1970's-early 1980's

Please help me remember the name of this movie:

I remember the jist was a family that either rent a summer house/cottage or trade's staying there for caretaking the grounds. There is an Aunt or something that stays in the attic by herself with a bunch of pictures on a table outside her room.

The family is a couple and 2 kids, boy and a girl, one of which the pool (i think) almost or does drown. The longer they stay the crazier everybody gets. The mom stays outside the door talking to the aunt and ends up 'being' the aunt by the end....dad goes to rescue her at the end she's sitting in the aunts chair and hes somehow thrown out the window while the house is falling apart around them.

The only other thing about it I clearly remember is the people they talked to that were in the house before they got there....the male character was the guy from Ripley's believe it or not, but I cant remember HIS name either....do remember he died no too terribly long ago though.

I'm trying to purchase a copy of this, but it's hopeless without the name of the thing! Any help would be greatly appreciated.

Kelly