Is a person who dies of a chronic illness, with two openings in the lungs, considered a martyr, and do his mother's satisfaction, his good character, and his young age benefit him?

May Allah have mercy on your brother. His striving to please his mother and his good character are among his good deeds. We hope that he is among the martyrs of the Afterlife due to his suffering during his illness, and his death at a young age is better for him. Your vision of him is a good vision, so strive in supplicating for him, seeking forgiveness for him, and giving charity on his behalf.