Since she's a stray cat you could take the kittens and nurse them till you can find a shelter to adopt them - newborns are ready to adopt at 6 weeks and shelters find them easy to place. If you don't do this, they will grow up feral, starving, and perpetuate the cycle of starving stray cats in our world. I had a feral stray creep in through the cat door and have her kittens under my bed. I kept two of them, nursing them from newborn, and adopted out the other four. I still have those two cats, Kate and Fred, featured in my flickr site, and the others grew up to be gorgeous half-angora, half-tabby mixes, non-feral, with a healthy domestic kitty life.
Your post got me thinking: how did the mom cat get inside your car? One of my fears is that a mouse or, even worse, a rat will find its way into my car someday.
I'm guessing the top was "down."
Looked out my window last week and saw in my backyard, out cavorting under a hot summer night sky, a yellow momma cat and three healthy, lively kittens. ;D
Hey Del, how's the rest of your home ownership and all the problems you're dealing with going for you?
Goodness, you're in quite a pickle, aren't you? Filled with trials and tribulations.
Have you found any happiness or comfort at all in your home, or do you just want to run screaming from the place?
And why is your sister nagging you?
Has she helped at all?
I wish things could be better for you.