Perhaps you could use that feliway spray that's supposed to help in multi-cat households? This can do a lot sometimes with males spraying. I see Joey is neutered, is colin too? Sometimes that limits spraying, colin is obviously marking his territory, so perhaps you could keep joey separated for longer till colin gets used to his scent...I really hope it works out, Joey is lovely and It would be so upsetting if he has to go back to the HS and be put down