I would affiliate under the organization you would be training under most regularly (would that be 'B'?). The organization is just for convenience. It's your relationship with each of the senseis that matters most.
P.S. the plural of sensei in Japanese is "sensei-tachi", but that doesn't really work in English.
Thank you for the response. Practicality dictates going this route. I'm concerned with damaging my relationship with one of the instructors no matter which way I decide.