Paranoiac (1963)

Eleven years earlier, the wealthy Ashby family was shattered when Mr and Mrs Ashby died in an airplane crash and their grieving son Tony committed suicide. All that remains of the family is cruel Simon, an alcoholic in desperate need of funds; his mentally fragile sister Eleanor; and his protective aunt Harriet. Simon is just weeks away from receiving his inheritance, but there is a hitch in his plans when the long believed dead Tony Ashby suddenly arrives.

IMDb: https://www.imdb.com/title/tt0057401