Jayapataka Swami: Correction in the question that it was Duryodana’s son that wanted to marry Subadra. Since this was an interfamily dispute, they were all in the same family. So Lord Krsna had some relations with all of them. That means Balarama also had. So He allowed Lord Balarama to give some mercy to Duryodana. So it seems that the family was neutral. But since Lord Balarama could see that Duryodana and his brothers were acting impiously, they would be defeated. So he went on pilgrimage during the Kurukshetra war. He only appeared after the war was over. And then He objected that Bhima defeated Duryodana using some trick. But there was no other way that he could defeat Duryodana. So since Krsna is the Supreme Personality, He is the original Person, and Balarama is His expansion, just to add some variety to His pastimes, so They are manifesting some difference.