What film was based on Cain and Abel?

I would submit the answer "Amadeus".

The story of Amadeus becomes poetry and myth when one learns it is far from the official biography of Mozart. For in fact Salieri first became Mozart's lethal enemy in a poem by Pushkin, written 40 years after the great composer's death.

Robbins clarifies many historical inaccuracies regarding both Mozart and Salieri in the film, but proposes that playwright Shaffer and screenwriter Milos Forman have made the story a "myth better than history," a masterpiece of drama which reveals deep truths about the human condition. The film confronts the viewer with the sheer givenness of human inequality, the pride that gives way to envy, and the sometimes relentless character of efforts that may be finally deemed mediocre.

It is the mysterious story of Cain and Abel: one loved by God, the other for whom God had, inexplicably, "no regard."

https://the-artifice.com/amadeus-and-the-mark-of-cain/

Cain's eldest son was Enoch. I don't think any children are mentioned for Abel, so it might be Film = (Son of Cain) + Abel rather than Film = Son of (Cain + Abel) or Film = (Son of Cain) + (Son of Abel). Sorry to get mathematical...

I would agree "East Of Eden"

The book explores themes of depravity, beneficence, love, and the struggle for acceptance, greatness, and the capacity for self-destruction and especially of guilt and freedom. It ties these themes together with references to and many parallels with the biblical Book of Genesis (especially Genesis Chapter 4, the story of Cain and Abel).

https://en.wikipedia.org/wiki/East_of_Eden