Hi again, Pam and thanks for your very helpful reply.
The girls are afraid that Packer is an 'intruder' and there, to take over their territory. They're trying to assert their 'Top Cat' positions and let him know he has no power here. This is a very common reaction in new cat introductions. The unfair part of this, is that Packer is declawed on all four paws and the girls have all their claws, so he can't even defend himself, except with this teeth, but that means getting his face too close to their claws.
You did every right in having them get used to each others' scents and right now, you can take a slightly dampened cloth or paper towel and pet Packer, then pet one of the girls, then pet Packer again, then pet your other girl and pet packer, then vice-versa. If their scents are on each others' coats, they will smell each other all the time. You also could take an old t-shirt or other piece of clothing containing your scent and pet them all with it, so they smell your familiar and comforting scent.
Get some Feliway plug in diffusers; these emit calming cat pheromones that help to dial down the stress and anxiety. It has no scent to humans; only cats can detect it.
Try feeding them cat healthy treats on either side of the door. Eating is a pleasurable experience and you want them to associate good things with each other.
You an also try playing with them with an interative toy like a feather wand or fishing pole toy. You're supervising the activity, so you can watch for any fights. If they start going for Packer, gently push them back with a throw pillow and say 'No!'. Don't shout, but say it firmly. If you have a helper, this is better, because, let's face it, right now, it's 2 against one and that's not fair to Packer.
Here are two webpages with great tips and techniques on new introductions. It's never too late to start from square 1! : )
If necessary, and I always suggest this as a last resort, discuss with your vet, an anti-anxiety/anti-depressant prescription medication at a low dose, do help them feel calmer. It might be best to give them all, the medication, since everyone is on edge.
I agree that it's not right for him to live his life in one room. Try some of these other ideas and this does take time. If you feel you're seeing no forward movement at all, unfortunately, you will have to consider re-homing him to a home with no other cats. If it comes to this, first, think of relatives, friends, neighbors who are cat lovers and experienced with cats. Otherwise there are Cat Rescue Organizations that will take him and find him a home. Never bring him to a shelter unless you know for sure, they are a 'no-kill' shelter.
I hope they will eventually get used to each other and for now, continue to keep them separated when you're not home. They don't have to be 'best friends', but if they can tolerate each other without fighting, this would be great!
I hope this helped and please keep me posted, if you can, on how they're doing.
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