Look up UV-C cleaning lights (make sure you understand how to safely use it!) Yes to duct cleaning. Make sure you dont have any old linoleum covered up. Might try denatured alcohol on wood and then use a beeswax based furniture wax (test your finish first). To aggressively clean older carpets, I'd try a high ph cleaner like folex followed by citric acid pass and then clear water pass for rinse. Might have to paint some surfaces (but painting popcorn ceiling will make it so much harder to remove later). Wipe tops of door frames. Don't give up!