HELP! I'VE FOUND AN INJURED CAT ON MY FRONT DOOR!?

I think you should get help from a friend and wash it up first. You must be a human first and treat it with some antiseptic water meanwhile be kind enough to call the Animal Care Service or something similar to that in your area. Cats don't get AIDS and you shouldn't fear getting that and your parents shouldn't be so inhumane. I wish I were in your shoes!!