Eliquid is composed of pg//vg, flavoring and nicotine. The amount of flavor and scent is controlled mostly by the amount of flavoring. The amount of vapor (produced by pg) can also add to the flavor and scent. Lots of vapor = more flavor and scent. If the liquid is 70pg/30vg it may help to get a blend that is closer to 50/50.
Be certain he is using quality equipment. If he is using a cheap bargain store clearomizer he may be missing half of the taste, sensation and nicotine. Also, make sure he knows how to adjust the variable voltage to the sweet spot to get the most from the equipment.
Depending on which chart you look at 12mg is considered light to medium. I smoked ultra-lights. 12mg works for me. He may be chain vaping because he is not getting enough nicotine in his system. Get bottles of 18mg and 24mg to see which works. Try a flavor with more of a vanilla flavor than strawberry. Vanilla should not be as annoying as strawberry. Unflavored with a drop or 2 of menthol, mint, cinnamon or a different fruit.might work. A bakery flavor - banana nut bread, pie or cookies.Try to get him to rotate at least 3 flavors. More is better. By vaping the same flavor repeatedly he may be setting himself up for Vapors Fatigue (vapors tongue). I've had it for over 2 months. There is no fun in vaping with the loss of the sense of taste and smell.
Get a portable air purifier with a HEPA filter. Read the labels to be sure the filter will remove smoke and odors from the air. Do not get a silent purifier as they do nothing to pull air in. 3M Filtrete filters are excellent. You may need to cut a 3M filter to fit the purifier. Put 3M filters in the AC system and furnace. Leave the fan running to pull the air into the AC filter. Place the portable unit in the direction where he exhales.
Good luck!
ETA: Stealth Vaping: The liquid, not the equipment.
https://www.youtube.com/watch?v=jy0FJ-RWcNo