Back to the question..... I lost my old cat 3 weeks ago to kidney faliure, he deteriated over a month he went from eating loads as he normally did to then drinking gallons, i took him to the vet they did the same with my cat has they did with your friends, he decided after about three days he had had enough and did not want to eat, there comes a time..... when you know that they have had a great life lived for 18 years and thats over a hundred in people years that its there time, mine would not want to have suffered so i did the kindest thing and put him to sleep, its very very hard but i think i did the right thing by him,
good luck