I think overall this are great renders.
Things that I believe can be polished:
In car: Add a very soft blue light behind the chairs, to me it feels like there needs to be more environment light, and it gets a little too dark. Their fur also feels wet or too thick to me.
The road: The windshield glass I think is too perfect I suggest adding imperfections to the car and the condensation can be tweaked to be more subtle on the glass.
I would also exaggerate the poses more of the two mice. The younger ones face more visible with his head tilted more out the window, and the older mouse looking like he is making more effort to get it started.
Also car license plate? And grill to have a more metallic defined look.
Hope these comments help!