I can't think of a single character in the book for whom nihilism is their defining trait, and certainly not the primary characters. The effort to preserve goodness in the world only really matters when it's hard, when it comes at cost. The book turns that up to 11, but that is why it is hopeful.

If you want to read McCarthy doing nihilism, maybe try the sunset limited.

"You give up the world line by line. Stoically. And then one day you realize that your courage is farcical. It doesn't mean anything. You've become an accomplice in your own annihilation and there is nothing you can do about it. Everything you do closes a door somewhere ahead of you. And finally there is only one door left."