Hi there, I have a cat that we adopted some months back who is an excessive groomer due to stress and I have found that Feliway plug in seems to help. It's alot like a Glade plug in air thing but it has artificial pheronomes that help to calm cats when they are stressed. You just plug it in to an outlet in a room that the stressed cat spends the most time in. You can get it at a vet clinic without a prescription. It also comes in a spray. And you can get a cheaper version of it at the big petstores.
You might want to try Rescue Remedy, it's a tincture you get at the health food store. Pet stores have it too I think under a few different names. You put a few drops into the drinking water and it helps calm them.
I would agree with Karen that if you can turn your kitties into indoor cats on a permanent basis it would be the safest option for them. Apartment complexes have so many people coming and going and not everyone is good to animals.
We've moved quite a few times and we have one cat that gets pretty stressed about it and we have found that if we can duplicate her favourite room which happens to be our bedroom, she settles in and begins to feel comfortable. So, the first thing we do is set up our bedroom in almost the exact same layout that it was in at our previous home and she seems to find comfort in the familiarity of it.