The story of Cain and Abel is perhaps one of the most famous Biblical narratives in the Book of Genesis. As an etymology, it deals with, among other things, the origins of jealousy, envy, wrath, hatred, and murder (specifical fratricide). This allusion shows up in Final Fantasy from time to time.
First, the story:
Adam knew his wife Eve intimately, and she conceived and bore Cain. She said, “I have had a male child with the Lord’s help.” Then she also gave birth to his brother Abel.
Now Abel became a shepherd of a flock, but Cain cultivated the land. In the course of time, Cain presented some of the land’s produce as an offering to the Lord. And Abel also presented [an offering] – some of the firstborn of his flock and their fat portions.
The Lord had regard for Abel and his offering, but He did not have regard for Cain and his offering. Cain was furious, and he was downcast. Then the Lord said to Cain, “Why are you furious? And why are you downcast? If you do right, won’t you be accepted? But if you do not do right, sin is crouching at the door. Its desire is for you, but you must master it.”
Cain said to his brother Abel, “Let’s go out to the field.” And while they were in the field, Cain attacked his brother Abel and killed him.
The first takes place in Final Fantasy IV. Kain shares a variation of the name, Cecil shares the alliteration. Kain’s susceptibility is probably due to his jealous and envy of Cecil’s and Rosa’s love for each other. Later, Golbez and Cecil, actual brothers, will enact the story of Cain and Abel.
The second is a bit more reminiscent of the story. Kuja was the first born and deemed a failure to Garland (who represents God). He creates Zidane, Kuja experiences jealousy. Feeling threatened, Kuja kidnaps Zidane and leaves him on Gaia presumably to die.
The third includes the twins Gabranth and Basch. The former frames the latter in a Dalmascan plot of treason.