It is always hard to make a decision like that and second guessing it won't help. The poor thing was 14 years old, had been suffering for some time and although it hasn't been mentioned yet, along with all that, he lost his human (your husband's uncle), he lost his home, (the farm) and he had a lot of medical problems. He had too many counts against him and your Vet must have figured that out too. I don't know any Vets that enjoy putting an animal down and if he was a "bad" Vet, he would have kept him around and taken you to the cleaners financially with the same result.
You did the best you could and you gave him the best care you could under the circumstances. My hats is off to you and my prayers are with you and your family. You did your best and that is all any of us can do.