How can I keep my parent's room smelling fresh?

A little bowl of charcoal under the bed or even a box of baking soda just opened up in the corner.

Use the containerized room sprays sold at Yankee Candle. Very effective.

Oh my gosh, that odor. With my parents house it was because they never opened a window to get fresh air, and issues with not getting to the bathroom on time, even wearing Depends. They became nose-blind to the smell.

So in my house, I always have at least two windows open a bit, even in bone chilling weather. Plus, I do something similar as KatyKat had mentioned above... for me I take a green Zest soap bar and place it in a decorative container. Every now and then there is that whiff of nice smell. Experiment with different soaps. I keep the container at the front door entrance.

One time I used scented powder for rugs, then you vacuum over it. Never again, back 35 years ago one of the cats had trouble breathing and was rushed to the vet. She survived, and that shaker of rug powder got thrown out.

Hepa air filter. Ozium airisol spray as long as nobody breathes it in. unsented heavy duty febreeze. And cleaning. The never ending cleaning.

Borax works wonders on clothing as well. I use it on all my grandma's bedding and clothing to keep it smelling fresh. That might help as well. Good luck!

You might find some inspiration in this article and the following comments:

www.agingcare.com/articles/old-person-smell-174839.htm

Take a little bi of borax combined with some soap shavings....put it in an open container (like a small Tupperware container). Slide the whole thing far, far under the bed where no one but you can ever reach it. The room will smell fresh for weeks.