It's great you have a vet to get advise from. It's a shame you fell for the big box store scam that is their reptile sales. I am so sorry you had to experience that for your first snake. If I could I would ban petco and petsmart tomorrow from selling any living animal but that still has a long way to go to happen.
You are right you have two options
1 Assist feed until you can see if it will feed on its own or give it to a rescue that can do it. There is a chance that once you get a good feeding down it might learn to accept rodents on sight and not on sense.
2 Euthanasia. This is not failure, it is mercy
I am sorry your son is involved but this is part of life with owning reptiles and its a great life lesson to understand that sometimes you have to let go.
Good luck and it is not your fault if you have to give up.