I mean they need to respect YOUR schedule on this and work around your professional career not the other way around.
I will say this from my own experience, they are family. Some day they will all be dead and you will wish you could take photo sessions with them.
Reading this thread really makes me appreciate the relatively warm winters where I live.
Your hourly rate is 14.50 USD?!
And the per car that seems really low. My local dealers will have like 15 pics of a given vehicle. I’m assuming to set everything up, figure out your compositions, take enough photos to get 15 good ones, editing and delivery would be like an hour of my time.
That said if that’s what you charge and you can live with it I have to think you are going to be in high demand and never lacking work.
Sony 24 to 70 2.8 GM II