Personally, I would rather ruffle a whole lot of feathers and lose the cost of fees, hotel, etc. than leave my pet who has been a beloved companion, in her time of need. But I understand how much this means to your son and that's important too.
¨I spoke to my AH and he said he will do what is humane if he feels she is suffering.¨
Can you really trust an A to do the right thing? So if you have to go, and you do for your son's sake, PLEASE make an appt. with the vet to come to the house and take care of your dog as soon as possible. Don't wait until you get back, don't rely on your AH. Do this for your beloved friend.