Satanás de todos los horrores (1974)

A traveler arrives at the Gerard mansion to visit his old friend, Eric Gerard. Upon arriving, however, he discovers that Eric and his sister, Isabel, have been afflicted with a mysterious malady: Eric's senses have become painfully acute, while Isabel has become nearly catatonic. That evening, Eric tells his guest of an old Gerard family curse: any time there has been more than one Gerard child, all of the siblings have gone insane and died horrible deaths. As the days wear on, the effects of the curse reach their terrifying climax.