Can't really answer that question.
The only humane way to perform euthanasia is with the intravenous solution administered by vets. This is why no experts have taken your question.
They will not answer.
Absolutely, he must be taken to a vet. It's very fast and ensures no complication or suffering. Morphine. Even excessive doses wouldn't just stop the heart.
Can't use morphine.
I am sorry for your situation, but I can only recommend the vet visit.