I'm so sorry that your family and Jake are going through this
I know what it's like as my little Brody had advanced kidney failure. It seemed like it came on so quickly for him. I'm not familiar with those medications although our vet did give us some type of heart pill that she said might lower his BUN. It did a bit but the name of it has slipped my mind. We did the sub-Q fluids twice a day at home, the k/d rx food, 1/4 pepcid per day and appetite stimulant as well when he wouldn't eat. It seems like your vet has him on the right track but I'm sending prayers and hugs. It sounds like you care very much about his well being and you are lucky to have each other. I know it's always hard to see your little one sick. Cherish the time you have together and stay strong.