Prince Andrew deployed to the Falklands in the summer of 1982, and Queenie let him go (but, then again, he wasn’t the Heir to the Throne...)
No - at the time Prince Andrew was, himself, the “spare”.
Practice is that either the heir or the spare can be allowed to serve in combat situations - not both. The Prince of Wales was out of the Navy by 1982 anyway, but if he had still be in operational service, they’d have had to resolve the issue there.