I am glad to hear Beau is "only" dehydrated. I am sure he is feeling much better already.
I am sorry about your vet bills. Looking at the headcount of your fur family I can develop a rough idea about it.

Since Filou is getting renal food both of our boys have become very spoíled. And Royal Canin seem to be the only ones that manage to get a taste in cats like- even Tigris likes the dry food. But of course Filou tries to sneak in and get any treat or rest of butter from the plate or salmon or.................

All our best thoughts for Beau- he looks so heartbreaking old and cute.