Travel for Maintenance of Short Term Rental

My spouse and I own a short term rental 300 miles away.  We travel there periodically mainly to maintain the property.  Mileage is obviously deductable at the standard mileage rate.  When it comes to food, can I deduct two times the standard perdiem allowance for the travel days and the days we were working at the property? 

 

I already know that 50% of the time must be spent working on the property for the trip to be considered work related.  I assume that means at least 4 hours a day for each of us.  I would guess if one of us works 6 hours and one of us works 2 hours then only the person working 6 hours would get the perdiem for that day.  Is this correct?   Or is it allowable to just estimate for the whole trip that person A spent 60% of the time on work related activities and therefore gets to deduct 60% of the daily allowance.    Or do they get the whole perdiem for the trip since they worked >50% of the time.   I'm confused on this prorating of the perdiem and mileage.

 

For the mileage, if 75% of the time was spent on work related activities, then do I need to prorate the mileage also?

 

If I stop 1/2 way to visit a parent for a few days, do I need to make sure that the days spent there are less than the days spent working.  Alternatively, can I start the business trip at the parent's house on the day I depart from their house and just claim the mileage from their house to the vacation property?