My first cat is slowly losing kidney function.

She's gone from 12 lbs. to 9 lbs. in the past year.
I have to bring her in today for a 3-day IV to flush out her kidneys, then she'll have a subcutaneous tube put in so I can load her up with fluids periodically to keep her kidneys flushed out and working.
She's not even 10 yet!
Anyone else have to deal with this with their cat? It's going to mean prescription food, and that means prescription food for 4 cats since there's no way to feed them separately (or keep her from eating the wrong food).