I just want to make sure that at least one person tells you this. You have no obligation to care for these animals. Wild animals get injured and die all the time. You can't save them all.
It already sounds like these animals are putting a major stress on your life in both time and money. People can get really weird about wild house pet animals, and will assume you care about them as much as they do. Which I am sure you do.
The TNR advise is solid if you want to get involved, but please for the love of God do not go into debt 'saving' this kitten.
You sound like a great person. Don't do anything you are not comfortable with, but sometimes the best thing to do is let nature take it's course.
Seviper, big doofy snek