This one is profound... I have many cats, ages 15 down to less than one year. In March of this year, all of my cats witnessed a stranger break into my home and murder the Alpha Male cat in a brutal manner. That really traumatized all of them badly. Thankfully the oldest male, who is the most gentle giant you could imagine, took place as Alfa male and comforted the rest back into a feeling of security. But then, on 5/27/08, he got sick and my husband and I treated and monitered him, in the presence of the rest of the cats, for what appeared to be vomitting and lethargy. The other cats could tell that he was dying, but we could not, he was only 8 years old and no known health problems. Long story short, we took him to the vet only to find he actually was dying from heart, kidney & diabetes, which we were totally unaware of. He had to be euthanized quickly due to a massive fluid buildup around heart and in his lungs. So once again, the rest of the cats witnessed another horrible event involving an alfa male. Since then, they have all been out of sorts, confused, scared, depressed, lethargic and all signs of grieving. I got advise from my vet and all over the internet on how to deal with grieving cats, but since this situation is particullarly brutal, nobody really has advise on such a large scale.
I know this situation is unique, but if ANYBODY can offer anything, or has had a similar experience and came through it successfully, please guide us, I am afraid that there is a domino effect going on, as most of the remaining cats seem to be in decline. I would appreciate any words of advice, even if you think that I may have heard them before. Thank you, and wish us all luck.

Is it possible that your declining cats are sharing an infectious process? Given love and support, daily petting and attention to all of them, they should pick up their normal social order in time.

Give it time and someone will step up and be the leader. There are afew things you can do to make the cats see which is the leader. Which ever cat is to be the leader always feed and pet him first.
And as for the cats grieving it is possible that you yourself are still grieving or that you are expecting them to be sad and depressed and so they act according to your emotions.

They do have their own "pecking order" certain cats will hog a food dish, a toy, a nice spot on a window sill etc. Certain cats will team up and boss a bigger cat that neither of them could boss on their own. They will all have to adjust to the new situation in their own way. I know it is hard, for instance, maybe if a mother cat has a superior son, she gets to be the "queen bee" and everybody else has to respect her because she will complain to her son if they don't. And if she loses him, she's no longer as important. I think this is part of the problem between wives and mothers in law sometimes!

Cats definitely will sense your emotions and may be picking part of this up from you. As you heal (and what devastation!), they may start to heal also. wildandblue is right that they need to adjust in their own way, and re-figure their own pecking order. I would let them do this and not interfere with it. (Unless one's going to seriously hurt another.)

One thing that is supposed to help is sticking to routine. Cats are very much into routine. Not only may they have had a shock, but also their routine has been disrupted. So do as much as possible exactly how you've always done it, which should help comfort them. Give them love and attention, but don't do anything extraordinary that's too far out of normal. They need to stick to what's normal.