Cain and Abel were the only two sons of Adam and Eve in The Bible. Cain killed his brother Abel and was forced to wander the earth.
ANOTHER ANSWER:
The "third son" of Adam recorded in the Bible was "SETH." But Adam's genealogy doesn't detail an exact number of Cain and Abel's MANY OTHER BROTHERS:
"When Adam was 130 years old, his son Seth was born, and Seth was the very image of his father. After the birth of Seth, Adam lived another 800 years, and HE HAD OTHER SONS AND DAUGHTERS." (Gen.5:3-4 NLT New Living Translation)
The only question that remains is: "How many children [sons and daughters; brothers and sisters of Cain and Abel] is it possible for a man have in the course of 800 years?"
Yes, at least one other brother Seth (He was born after Cain killed Abel).
Seth
Cain and Abel were the first two sons of Adam and Eve. There were no other people on the face of the earth at that time. Cain murdered Abel and then fled to Nod. The only logical explanation for Cain's wife is that Adam and Eve had sons (Seth) and later daughters, and Cain married one of his sisters. Cain had a son by the name of Enoch (Genesis 4:16-18).
Abel was this first little brother. His brother's name was Cain.
Their brother's name was Seth, but he was born a few years after Cain killed Abel, and he was banished for his crime. (Genesis 5.3)
Abel was Cain's brother, that he killed.
Cain took his brother to the field ... where he murdered him.
Cain is Able's younger brother. In the Bible, they are two of the sons of Adam and Eve. Cain is known for killing his brother Abel out of jealousy.
Cain from biblical times was the first person to kill his own brother Abel. The fratricide was committed because Cain was jealous of his brother. He even said, "Am I my brother's keeper?" when the Lord asked him where Abel was.You can read about this in Genesis Chapter 4.
Cain. KJV
According to the Biblical story, Abel was the second son of Adam and Eve. -Second son of Adam and Eve -Cain's brother -Cain killed Abel here's the story if you want to read it all http://www.dltk-bible.com/genesis/chapter4-cv1.htm
Abel
Abel
Because Claudius killed his brother {( Old Hamlet)} just as Cain killed his brother {(Abel)}