Vodafone 6 months sounds too short unless if it was an internship, probably you will have to explain why.
If you have been the last 4 years in the family business I do think that both letters should be related to it, it is where you have spent your recent time so the ones that are most updated about you.
About your uncle's previous titles I do no think that would make a difference if he has not interesting insights about you and your potential.
If he does then maybe is better than someone that also has them, but unless he is a relevant donor for a school endowment (and even if) should not make a difference because of his status/position; if he holds an MBA or is an alumn of the school could be more relevant.
Regards,
Pablo