My heart goes out to you right now Lisa. Are you dealing with FIP for sure, or could this be cases of Panleukopenia? It's highly contagious with a high death rate.

http://www.petcaretips.net/feline_panleukopenia.html

I just wish there was something I could do to help you and ease your pain. You are in mine & Kevin's thoughts at this terrible time. XOXO