How many son did Karna have? Is Sudama one of his sons not present in Mahabharat war? Did he die before the war? If so who killed him and why?
In an answer at quora here it is said no such character was ever present.
"No such son is either mentioned or killed at Draupadi’s Swayamvar in Vyas’ epic. This character was in all probabilities an invention of Shivaji Sawant in his legendary mythological fiction ‘Mrityunjay’."
And the same asserts wikipedia
Karna have other sons Vrishasena and Vrishakethu, Sushena and Satyasena.
The two protectors of Karna's car wheels, viz., his two invincible sons, O sire, that were named Sushena and Satyasena, began to fight, reckless of their very lives. The eldest son of Karna, viz., the mighty car-warrior Vrishasena, himself protected his father's rear.