So sorry to hear about the issues with some of your clutch.

There's no "comfortable" way of euthanizing a ball python. The most humane way is the messiest - total instant annihilation of the brain. Gasses don't work well because they have such a slow respiratory rate. Decapitation is inhumane because the brain can survive too long without a body. Freezing is inhumane because they don't just fall asleep like people do - they allegedly feel their blood cells crystalizing.

Some people practice pithing, which involves inserting a rod into the skull and scrambling the brain. Though it's been mentioned, I've yet to see any type of in depth instructions, so it's best that it be done by someone who isn't squeamish and had a solid understanding of ball python anatomy.

I do not know if a vet would pith - my guess is they would inject the snake with some kind of drug combination to seize the heart.

It may be worth a shot to feed the kinked hatchling, just educate yourself on what the risks are (i.e. regurgitation, ruptures, sepsis, etc.) and make an informed decision. I'm in favor of supporting viable life, but there is a point where supportive measures become cruel when the life is ultimately not viable. Use your best judgment, and keep in mind that surviving isn't the same as thriving.