[can't think of move title!]

Thank you soooo much! It's been driving me crazy for the past several weeks!

[can't think of move title!]

Can you please help me? The movie is about a woman with 2 sisters who are a little off kilter. She brings them to visit her while she is being a companion to an older lady. She ends up killing the owner of the house and hiding her body in the oven. I think it's a british movie. It's black and white.