my theory: N's family either founded team plasma in the middle ages or they are high ranking members. N left tp because he didnt agree with the way they ran things, so he left to pursue the same goal, but a different way: instead of using Reshiram to "free" pokemon, he wants to use zekrom to "free" pokemon(and reversed in the other version). and about half way through the story tp has a coup or impeaches N's dad(who was the leader) because he lost to you. so N's grandfather/uncle crowns N's sibling, who has it out for n because he left tp, the new leader of tp. so eventually you make N see the error of his ways and you team up against tp to defeat them