Narcissa was always the perfect daughter because she wanted to make her parents proud. She wanted to make up for all the stress that Bellatrix and Andromeda caused them. She wanted to be noticed for the "right" reasons. She wanted to be a "proper" Pureblood because anyone who wasn't proper was scorned and hated.
Lucius hated his father, but in public he was always the perfect son. He knew the consequences of embarrassing his father or doing anything to shame the Malfoy name. It was easy to hide secrets behind the walls of a huge manor.
Narcissa was a quiet student who never gave the professors any problems. She was above getting in trouble.
Lucius was always the perfect student. He was charming to his professors, never showing any anger or frustration. He was better than that. Unlike Mudbloods and Blood-Traitors, he had self-control and he could control his emotions.
Narcissa did her homework and she practiced everything that she was taught. As a Pureblood, she felt like it was her duty to do better than Mudbloods.
Lucius always excelled in his classes. His father would not accept anything but the best from his son and heir. Besides, the Mudbloods could not be allowed to taint the Wizarding World even more than they were already doing by doing better in school than a proper Pureblood. It just wouldn't be right.
Narcissa was always perfectly composed in public. Emotions were a weakness that could be used against you, and Narcissa was determined that no one would ever have anything that they could use against her.
Lucius's face was always like stone. In fact, everything about him was like stone. He could not afford to be weak in any way. He had to be strong in order to survive. There were enemies everywhere, enemies waiting for him to finally stumble and fall. Lucius was determined not to give any of them that satisfaction.
Narcissa still remained perfect in public even when her world started to fall apart all around her. In private, however, she finally allowed herself to break down and cry. She was always careful, though, to make sure that she once again looked perfect before she stepped outside her bedroom.
Lucius knew that it would only be worse for him and his family if he didn't give the Dark Lord the proper reaction to his torment and abuse. The Dark Lord would not tolerate any disrespect. He would not tolerate any of his servants not accepting their proper punishment. Abraxas Malfoy had taught his son well. So, Lucius cowered, even though it inwardly shamed him. He would be the perfect sacrifice. He would be the perfect object for the Dark Lord to inflict all his rage upon. Even if Lucius could no longer do much in his current position, he would do his best to protect his family from suffering that same rage.
Narcissa had always wanted to be the perfect mother. And that was exactly what she was going to be, even if it cost her everything. She was not willing to sacrifice Draco, not even for the Dark Lord. Narcissa had never been the perfect servant like Bellatrix had always been, and Narcissa had come to realize that it was impossible to be perfect in everything. But that no longer mattered to Narcissa. All that mattered to her was that her family survive the war.
Lucius had always hated the perfection that his father had always expected out of him, but he had always been perfect at not showing that. Always, however, was a very long time; and nothing could last forever. The Dark Lord had learned that the hard way. As for Lucius, he was just glad that Narcissa and Draco were all right, and he no longer cared if the world was able to see that. They had all survived the war, and that was all that really mattered to him.