Josette, I'm sorry that you and your fiance are going through this. The steps that your oncologist gave you are the same as I was given last year. Chemotherapy can affect kidneys, sometimes causing fluid buildup around the kidneys. Cisplatin was the chemo that did this to me. The oncologist may try one or more medications to help protect the kidneys from the chemo. If the fluid build up continues, he may recommend the nephrostomy tubes, which drain the fluid into an external container. If the nephrostomy isn't done and the kidneys get worse, the oncologist may stop the chemo and schedule the cystectomy sooner (which is what happened to me). (By the way, following the cystectomy, I've been cancer free for 18 months.)
Dolphin83's suggestion to get a second opinion is an excellent idea.