There is an incredible amount of confusion about how party skills work. While the wiki link in official wiki almost seems to get it right I believe that this part is wrong
"If the player character and one other companion have at least level 2 in the same party skill, a bonus will be awarded to the total level."
I am almost sure that the bonus stack itself on a leader. So for instance if you as a leader have path-finding skill 10 which bestows +4 leader bonus to the skill, you don't have to have some other companion having path-finding 10 to get the total value 14 for this skill.
So the wiki entry should read like this
"If the player character have at least level 2 in the party skill, a bonus will be awarded to the total level of that skill. The party member who has the highest level in that skill will determine the party skill base value, while the leader will grant level bonuses according to the chart:
Skill Level Bonus