I have been in your shoes way to many times, though the decision is never easy I always follow my pets lead. If they are in pain and suffering I put them down if their is nothing the vet can do. But first I spend a day with them feeding ( if they eat) them their favorite foods, anhd doing some of their favorite things ( if they can) I hold them while the vet puts them down and tell them how much I love and will miss them. My heart hurts for you and hope you will know that their are those out here who understand.