Help! - Have a Bunch of Cats Living in an Old Car

I have an old car way back on the back of our yard/property. There are
at least 15-20 cats living in it. Some of them look to be fairly
healthy. I'd like to get rid of them. I assume I could just take them
all to the pound, but it would be a lot of trouble to somehow round
them all up. How can I catch them? A lot of these cats are pretty
skinny and kind of matted-looking.

Some will come up to you, but I scare them away because I'm not sure
if they have diseases (we don't have any cats ourselves). I've also
thought about getting a large dog to maybe run them off. My son and
his friends throw rocks at the car and a lot of them will run off for
a time, but will be back before nightfall. (My son is the one who
alerted me to the cat problem.)

Any ideas?
Buzz