It is a very big leap from an inhibited nip/bite to a proper bite.
My 12 year old dog has terminal bladder cancer. Her symptoms and pain are managed and she currently has excellent quality of life. She started nipping when being prodded in her belly by the vet when they were trying to diagnose her as it was very tender. She now guards her belly against hands even though she is painfree, and will nip if people touch her.
Because of this I keep her separate from all children, including my own, just in case they inadvertently hurt her. It is not fair on the children or the dog to put them in a situation where there may be a reaction.
If she ever bit anyone on the face, or drew blood, then she would be PTS. Hard as I absolutely adore her - but IMO there is a line, and that would cross it.
Your DH did everything right, bar ignoring the growl. You initially said you thought it was because he hadn't spoken to the dog - he has since told you he was speaking soothingly to it, and still it reacted aggressively.
Despite everything you have done, and it sounds like you really have done everything, your dog is becoming more aggressive, not less.
You are making excuses for the dog, and I think you know it. I completely understand why you are doing it, I would too, but the fact is your dog is aggressive, and he is getting worse.
FWIW my friend lost the sight in one eye when his GF's normally friendly JR took umbrage at him bending over to get something out of his bag. He hadn't done anything to provoke the dog, it just launched at him, bit his face and his eye just happened to be where it's teeth met. This could have been your husband had the angle been different - and this could be your daughter next.
I think if you have tried SO hard, and the result is a worse bite than previously it's time to put your family's safety first.