Some things i found...
Maybe u read sth which can help u..

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It certainly can start out as a flea allergy, especially if it is along the
back and tail, that is where it is hard for cats to groom properly and they
will rub their hair out in an effort to remove the problem. If it is
ringworm, it will floresce green under a blacklight. If it is fleas you will
find black flea dirt and sometimes only one flea if you use a flea comb

***

Several things can cause this condition. Fleas are the first thing to look
for. If they seem to be clear of fleas (no flea dirt or live critters) look
at their diet. A poor diet can also cause hair loss. Bordom is another
cause, get them active with toys and walks. If all else fails, a vet is your
next move. If your vet is expencive try the local shelters. They often have
vet services at a much lower rate. PetsMart also offers vet services and I
believe they are cheaper than most vets.

***

If your cats' hair loss is on the back of the legs and under the tail, first
consider any local orifices as the source of the problem. There may be
digestive parasites exiting in the feces, urinary tract infection or yeast
infection, all of which cause discomfort and itching. Water-bourne parasites
are also a possibility, since Vee likes to sit in dirty water.

Check the litter box for signs of adult parasites in the cats' feces, then
check the cats' anus for signs of irritation or parasite segments. Bring a
stool sample to your vet for analysis. It doesn't cost much and treatment
can also be inexpensive.

Cats have an oil gland under their tails which can sometimes become
occluded. It's rather bothersome for them and they end up licking themselves
raw. Your vet can evacuate the gland, but be forewarned that it'll create a
powerfully bad odor.

"DebbieWI" unter <debert@nospam.frontiernet.net> in
3534572602a400ac4446544b569ee696@localhost.talkaboutpets.com:

One other thing:  Your cats are old and could be close to dying.  I
lost my oldest cat (17.5 years) just after a lot of her hair fell out.
I ddin't notice that she was pulling it out and assume her systems
were failing.  This may not be your problem, but you should know about
it.

Saul Levy

My oldest cat is also a baldy cat!
We tried lots of diff hormone treatments, found one that did work, but she
developed a lump from it, and had to stop tablets and operate on her.
Now what the vet and I do, is leave her to it, but when i think she's making
herself sore, I take her into the vets she had a hormone jab and tablets for
10 days, this helps clear up the soreness.. and takes her mind off the
obsessive licking.
She looks like a right freak.. but we love her :)