The Malfoys want the battle to cease so they will know what happened to their son Draco. Narcissa lied because she wants the war to end and she knows that Harry is the only one who can end it. Thus, she save Harry from Voldemort because Harry said that Draco is in the castle, it's like a thanks giving for Harry.
She asked him because if Draco was still alive, she had something to fight for. She had a reason to lie to Voldemort. If Draco is alive, she needs to get into the school to see him and protect him, and helping Harry feign death was the easiest way to do that.
Draco did help save Harry, Ron, and Hermione by not identifying them to Death Eaters, which is a huge moment, but the most stand-out moment is when Draco is supposed to end Dumbledore's life. Planned all along by Snape and Dumbledore or not, Draco could not find it in himself to end a life.
Power wise, Cell started off at a level stronger than SS1 Gohan, but weaker than SS2 Gohan, and ended up being roughly on par with SS2 Gohan. Given that Super Saiyan 2 is stated to be twice as strong as the normal version, Cell probably became somewhat less than twice as strong as he originally was.
12% difference. If both are at 100%, and one's 100%=75% of Beerus, while the other's 100%=66 percent of Beerus, then the percentage difference between the two is 12 percent. Being that SSGSS is 50X SSG, then that means that SSJ4 is 12 percent weaker, then the strength of SSJ4 is 44X stronger than SSG.