CHeck this article on emissions from western hemlock during drying and why is causes some grief for lumber mill emission monitoring.

https://www.researchgate.net/publication/283614582_Emissions_from_western_hemlock_lumber_during_drying

Also, take a hard look at your cleaning products. With that much wood, if your using lemon pledge, murphys oil soap, paste wax for wood floors your adding more VOC inputs.
I've seen some people have luck reducing VOC levels with activated carbon air filters. Since you don't have a forced air system, you may be able to find a stand-alone air cleaner like this
https://www.rabbitair.com/products/biogs2-air-purifier
I'm not sure how much VOC it will remove, but it may be a quicker cheaper solution to your problem. A few replacements of the carbon filter and over time, the natural levels may come down to reasonable levels.