Personal Use on rental Property

[stellarun21]

My sister and brother-in-law own three rental properties in a city that is about an hour half away from their home/primary residence.

For the last rental property C they bought in 2021, it is not 100% rented to tenant; they save one room (about 20% of total area) for themselves. That way, they don't need to stay at hotel if they travel there to maintain or repair any of the rental properties because it does take quite a bit of drive. Of course, occasionally they do travel to that city for personal reason and stay at the room. Personal use days on that room are no more than a week. 

In this case, should they call that rental property C is only 80% business use and only place 80% of building/land in service and take only 80% of deduction? Appreciate your time and help. 

[MaryK4]

Yes, based on your description they should still use the percentage because even though their personal use would fall under the exception. Since it is not rented or available for rent, it should not be included as part of the rental.