We paid cash for a 3 unit building in 2020. Two of the units are rented at fair market value and one in used by family. How is this recorded in turbo tax?

[meshipley1]

Half my building is for personal use and half is rented for fair market value.  
Can I deduct half of all my expenses for this building?

[MSCO9241]

common expenses would be allocated based on square feet.   expenses specific to the rental units are deductible in full.

[Critter-3]

If it is possible that you or your family may ever use one of the other units then I highly recommend entering in the 2 rented units separately.  AND you will need to split the common expenses yourself ... do not expect the program to do it for you correctly.