I am a little confused on the context of your question....
However, the bottom line is there are potentially two separate interview processes when applying to USNA:
(1) Your BGO interview which is specifically for your USNA application -- this MUST be conducted (exceptions are delinquent interviews on the fault of a BGO)
(2) MOC Nomination Interview which is only for your nomination. This may or may not happen depending on the nomination requirements of your MOC. If they require an interview and you are applying to multiple SAs, they might only interview you once for all SAs you are seeking a nomination to OR they might make you interview multiple times -- it all depends on what that MOC wants to do and how their boards are set up. However, consult your official MOC documentation to determine their requirements or contact their SA coordinator to get clarification.
If BGOs sit on a MOC nomination board, they ARE NOT authorized to interview (or vote on) their own candidates. Bottom line, is if the MOC requires an interview (at least one) for a nomination, then you will have at least two interviews in the process for applying to USNA. Hopefully this answers your question?
Also, my understanding was that ALOs could not sit on MOC boards -- maybe someone can answer that. Even if allowed, it doesn't seem ethical for an ALO to interview their own candidates --- conflict of interest.