During the time he was living there, Reuben went and slept with Bilhah, his father's concubine, and Israel found out about it. These were the twelve sons of Jacob:
The sons of Reuben the firstborn of Israel. (Though he was the firstborn, his birthright was given to the sons of Joseph son of Israel because he had defiled his father's bed. That is why Reuben is not listed in the genealogy according to birthright,
The descendants of Reuben (he was Israel's firstborn son), men aged twenty or over, were recorded by name according to the genealogical records of their tribe and families. All those registered who could serve in the army
No. He is to recognize the firstborn, the son of the wife he doesn't love through the usual custom of giving him a double portion of all that he owns. The firstborn son is the firstfruits of his father's strength, and so the rights of the firstborn are his.