My partner taught at both chain studios in the eighties and nineties. We are considering entering a competition together, but I wonder if we can enter as an amateur couple?

Once you've accepted payment for lessons you are considered a professional.

Dance Pro/Am until you up your game or you should be dancing Rising Star.

I know 1 couple who tried dancing Pro/Am and both taught lessons for years. She considered a beginner since she had never danced Standard. Both of them took so much flack from the rest of the dance community they didn't try it again. The comp was more than happy to take their money to dance what ever division they wanted.

I know several amateur dancers who teach and accept payment for teaching lessons, and compete as amateurs.