That is brutal dude and I'm sorry you two gotta go through that. It's never easy but speaking from experience I know you bust your ass and give all for your pets. Sometimes the challenges are insurmountable and you sound like you're keeping a level head with their best interest, quality of life in mind. We had a rescue cat at work last year with something that sounds very similar. Cancerous tumor there and your just not going into the esophagus. We managed a Peg tube on him but again, quality of life. Just as much risk of dysphagia there and tube is not a long term solution. He became septic after a few weeks and didn't make it though. 12 years is quality time spent he's lucky to have had you. Take care of yourself man.