Since you own the vehicles your actual monthly payment is immaterial. You will either use the actual expenses option + depreciation or the standard mileage rate for each vehicle. If you start with the actual expenses you are stuck with the actual expenses option you are stuck with that option for that vehicle until you no longer have the property. If you start with the standard mileage option you can "flip flop" each year to choose the better option.
Read up here :
https://www.irs.gov/newsroom/heres-the-411-on-who-can-deduct-car-expenses-on-their-tax-returns
And chapter 4 here :
https://www.irs.gov/pub/irs-pdf/p463.pdf
