Okay, first off, you don't actually need to befriend Gisette or Jarrod if your goal is merely peace. Even if your MC has poor stats, you could convince Gisette to set up Jarrod/Sayra by just making the right choices during the conversation with her, then perform well during negotiation. If you succeed, you can get a happy ending with Clarmont.
If you want to support the rebellion instead, you need to choose to do so during conversation w/ Sayra in week 7, then choose to play confused innocent or mislead Gisette when the choice comes up. Mislead Gisette requires 90 manipulation and provides "good" rebel victory, but simply playing confused innocent can also lead to successful rebellion, just not as quick (and the game classify it as a "neutral" end. You can still get a happy ending with Clarmont).
If you supported the rebels actively but Clarmont still died during civil war, then you have failed in negotiation during week 7 day 5. For that, I recommend just following the guide aza linked to see what you can do. See week 7, and you need to increase "rebelallies" for rebel victory.