The items that are reduced to 50% pertain directly to the rental property itself.
If you used your vehicle for purposes related to the rental property, then you would claim the full amount instead of 50%. If there is a reason you would reduce it, such as you traveled to the property with the other 50% owner, then you would just enter half of the miles, etc. TurboTax will not do that calculation.
Keep in mind that to claim mileage on a vehicle, you need to be the owner of the vehicle.