Grammatically correct: a. He is a more better basketball player than his brother. b. He is the most good basketball player than his brother. c. He is a better basketball player than his brother d. He is the best basketball player in his family.

Grammatically correct: a. He is a more better basketball player than his brother. b. He is the most good basketball player than his brother. c. He is a better basketball player than his brother d. He is the best basketball player in his family.

Explanation

 "He is a better basketball player than his brother."

correctly uses the comparative form of the adjective "good," which is "better".