RE-introducing problems

Help! We have two siblings, Pebbles and Bamm-Bamm who have been together from day one. We rescued them TOGETHER from a shelter. Bamm-Bamm had urinary crystals and had to be at the vet for four nights, then we brought him home and Pebbles HATES him. He's so sad. We had no idea this would happen, so we've done everything totally wrong so far. Pebbles swats at Bamm-Bamm every time he walks near her, and Bamm-Bamm is urinating everwhere because he smells Pebbles in the kitty box.
Right now, Pebbles is in the "kitty room" and Bamm-Bamm has free reign even though he's the one peeing. We put another box outside her door with food and water for him because he likes to be right outside the door.
Is there anything else we can do? We are at our wit's end.
Thanks so much!

This is quite common and the reason is that vet kitty has brought back so many alien smells on his fur that his scent isn't recognizable to the other cat. Plus, vet kitty was stressed out and that changes his scent too.

Here are some tips:

If you wear a certain perfume all the time, spray it into the air, put your arms into the spray, rub your hand briskly then wipe your hands on a towel. Using the towel, rub down both cats briskly.

Or use a clean towel and rub them both down with it transferring scents

Give both the cats a bath (if there are no surgical incisions)

Take vanilla extract and put a dab on both cats under their chin, between their shoulder blades and on the base of their tail.
Do this three times a day.

Dear Hissy,

Thanks so much for your quick response! I'm going to try the towel idea immediately!

Thanks for having such a great resource for information. I had left a message at an animal behavior specialist's phone number, but I still haven't heard back, so it was truly great to hear from you so soon!

This happened to me too, but my healthy cat literally attacked the sick cat and chased him into a corner. I had to pull out the water pistol to separate them.

I did everything Hissy mentioned, plus I switched them out of the closed room every couple hours. That gave them both time with each other's smells and time with the family. it took a few days, but eventually they relaxed.

It happened to me too. My two kitties were best friends. Then Simon had to go to the vet for 4 days and when I brought him back, Max didn't want anything to do with Simon. I took hissy's advice about the vanilla. I did that for two or three days, and now everything is back to normal.