It is never a good idea to spray something onto mold-infested areas; yes we use bleach if the area isn't too big, but we sponge the areas no matter what size. Don't risk the mold spores travelling around your air exchange setup.
If you have mold on the drywall that you can see, you're probably only seeing part of the iceberg. Replace it...
What do you intend on doing with these walls once you're finished? Tiling them? Bear in mind that your cleaning efforts are temporary at best and will last a number of months depending on how well you do. Any children or senior citizens around? You've just raised the stakes in this gamble.
A 4'x8' sheet of drywall is around $12 or so. Tear down might take you a half hour. Replacement another half hour. Knowing you've done what the pros would do? Priceless...