If a knightly unit is within 12" of the general (let's say, a Bretonnian lord) and that an unit of peasants are at less than 6" of the knights, but too far away from the general to have his leadership, do they have Ld 9 as a result of being near an unit of knights that benefits from the general's Ld?

No, they can take either the general's leadership if he is in range, or they can take the leadership of any knight within range; there is no such thing as chain-leadership.