Laxman in mahabharata was the eldest son of Duryodhan and queen bhanumati. He was killed by Abhimanyu on 13trh day of war in chakravyuh formation. It was one main reason why Duryodhan planned to kill Abhimanyu for seeking revenge for the death of his son.
Laxmana was twin sister of prince laxman. She was married by krishna s son samba. Before marriage during the swayambar ceremony she was abducted forcibly by samba and later samba was imprisoned by karavas for his misadventure. By interference of Balram , samba was released and laxmana was married to samba with the consent of her father Duryodhan.