Help identify: 70s Axe Killer, gift-wrapped scalpel

[AJ88]

Please help me identify this movie. I only caught about 20 minutes of it.

A man was locked in a room by a brother and sister. The room was in their house but it was like a padded cell. The brother and sister were doing this for their father, who was catatonic in a wheelchair. They were "showing" the father their "prize" but the prisoner was shouting about the father not even understanding what was going on. Then the brother and sister tell the prisoner to open a small door in the wall and inside is a wrapped gift. Inside is a scalpel. The sister calls the prisoner "doctor" at this point.

Before this scene, the brother was shown holding an axe and there were axe murders earlier in the film.

Help! I want to see the whole movie now.

More info:

Before the man was imprisoned in the room he was driving with the sister. She is taking him somewhere to hide away from someone. He says something like, "But he'll know this place." She says she never took "him" here. It's night as they are driving and having this conversation. When they get out of the car there is this house that seems to be in an isolated spot. When he gets out he turns and sees she's holding a gun. Then the brother shows up. This was the scene before the prison room.

PS: I was watching a Roku channel--"B-Movie TV". They don't post any kind of a schedule anywhere so you kind of take what you get--it's just streaming, like a cable TV channel. If you miss the title you kind of have to Google what you remember, and this time I'm coming up empty.