Thanks so much for all your advice!!!
Unclegus, we are spending 2 nights in Edinburgh and then would like to rent the cars and leave right after breakfast to get to St Andrews as early as possible to look around. We have a tour scheduled of the golf course in the afternoon and then will have dinner there. The next day onto Craigellachie (Speyside) to take in a whiskey tour and I guess exploring Dufftown and some of the areas around there-spend 3 nights ( any suggestions appreciated) We are meeting up with 5 other family members there. We may take an afternoon and go to Leault Farm for a sheep dog demo- the one RS tour goes to- Then we (the 5 of us in 2 cars) will head to the Loch Lomond/Balloch area for 2 nights (staying at Innkeeper's Lodge) (not sure what is in this area) and end up at an airport hotel...turn in the car...for an early flight the next morning.
After all your advice, I think we need to leave our Airbnbs early in Edinburgh and head to the airport by taxi (just found out they are bringing the car seat for their little girl plus pack/go play yard, luggage, etc) so taxi is easier than tram) rent the cars there and then we can return them there too at no extra cost.
I really appreciate all the info and if you have any other suggestions, that would be great!