I am so sorry to hear about Neko and know your heart must be breaking
I have been thro this with 3 cats and Napoleon was at vets because he got blocked up and couldnt use the tray, he had only one working kidney. It was discovered that crystals that had formed round his pea size dead kidney had broken up and got into his bladder.
They operated to remove them and my one mistake was I think that I didnt bring him home when t he vet offered cos only a day after the op, I ws terrified he may break the stitches holding his bladder together.
He also had been having seizures for 2 years or so before but he was not eplieptic.
At the vets he also would not eat and when I brought him home he would not either.
They should have told me he wasnt eating and I would have brought him home earlier because this caused renal failure and sadly I lost him in 2011.
So I agree witth your vet and that Neko is best at home and also with the others that you will know when its time.
Enjoy those special days you have left with him because it happens very quickly as it did with Ducha , Napoleons brother. On his 19th birthday he had a dish of chicken but 2 days later he had stopped eating and I had to let him travel to the Bridge. He told me he wanted to join his brother and in 24hrs the little weight he had just dropped off.
Neko has had such a hard short life but your love and care have allowed him to be a happy and adored boy and he shows you his love with every paddle.
He will always have a place in yout heart