Since all three have it, it is likely environmental or contagious.

https://vetster.com/en/wellness/what-to-do-if-your-cat-has-dandruff-or-dry-skin

What does their vet recommend?

Eileen, I'm thinking it's environmental. My tuxedo sheds a lot and she's a house cat so I looked it up. Shedding can be due to dry skin from being inside. Plus, it's humid and not dry in the house but there's still a difference from being inside our out. None of them scratch out of the ordinary, but one day I had my readers on and the tux was in the windowsill behind me, and when I took a look I could see lots of white flakes in her black coat.

I brush them daily, and two others have flakes but not that much. I haven't seen one flea or tick this year which is amazing since we're in the country.

Might it be their diet?

And what about other types of animal fats like butter or chicken fat? Most cats like butter.

Does salmon oil stink?

Carol, diet plays a big part. Later i’m going to put the fish oil on my finger to see if the tux will eat it.

I use a hairball formula for my cat that has chronic hard stools. It seems t be petroleum oil with some kind of fish flavor. It might help with the flaky skin but it does cause loose stools so be careful. I agree with others, if they all seem to have the same problem then it might be time to see the vet.

How do you give the hairball formula to your cat? I think the problem is psychological. About a month or so ago I dewormed the cats and coated their pill in butter. It's worked before but not this time. Oh no, they remembered. I put the pill in their wet food and there wer tiny pill crumbs in it, so I had to do the process all over again.

I noticed when I gave each cat their wet food with oil, they could smell the oil as soon as their noses were an inch away from the plate. They're smart and they knew I was sneaking something to them.

Honestly, the flaking isn't bad on the other 2 cats, it's mild and normal & I was going to give them oil also.

I might contact the seller, a small business, and ask if I can use a syringe or if they need food with the med so they don't get sick.

The oil can be taken without food, but it can cause loose stools for awhile. Going to load up the syringe. All of the 1/4 teaspoon. :)

Have you tried Greenie Pill Pockets? They're yummy!

I have one long haired cat that likes people food, gravy. I can make a greasy chicken gravy and he'll eat a tsp, twice a day as a treat. My Bombay...has short hair, he sheds a ton. They both get brushed every morning when I get up, then they BOTH get a chicken Temptations treat and another one before we go to bed. OK...several. :0) I think those treats are a dose of grease. I've never seen a skin problem.....don't know anything about it.

I brush them with a mans pocket comb so as not to take off too much hair. It's more of an enjoyable...getting attention experience than taking off hair. It may also help their skin, naturally...?

Cats can be so fussy!

I wonder if chicken fat might be more agreeable to them than fish oil?

What about eggs?

The hair ball formula comes in a tube like tooth paste. I squeeze about 1/2 inch onto my finger then smear it on the leg. They lick it off. You have to get it spread a bit on the fur so that they cannot shake it off.

We bought that formula at the vets but after getting it home and reading the ingredients, I threw it out. I wasn't willing to have my cat ingest petroleum.

If the cats have an oil deficiency, it would make sense to change foods. You shouldn't have to give cats supplements. Their food should supply complete nutrition.

Also, I have always heard that grains in their diet can cause allergic skin issues, so we feed grain-free.

I understand petroleum jelly has a laxative effect - that's why it works for hairballs - and causes loose stools as described above.

Since all 3 have it, it's probably environmental. Upgrading their diet is always a good thing. I'm over the top about this. I do a mixture of raw meat and meat that I cook for mine. Cooking is a LOT of work.

Cats need more fat than humans. You could try a small drizzle of safflower, sunflower, avocado or canola oil. I can't stand the smell of canola, but the cats will eat it. No olive oil. It won't hurt them but they can't process it to get value from it. Chicken fat and butter are good.

A simple upgrade is an inexpensive cut of beef for treats. Slice it thin as for stir fry. My cats like very fresh, but freezing will kill the things that might upset their tummies. Thaw and feed raw as a treat. (Never give raw ground meat from the store. It's not safe for humans, cats or dogs unless cooked.)

I only use petroleum jelly if the cat has a major problem with hairballs. My current ones don't, but that could change as they age. Supposedly it cannot be digested due to the length of its carbon chains. It should be inert in the body. I'm still not comfortable using it often. If you do use it, do so at least 2 hours before or after meals because it can interfere with the absorption of fat-soluble vitamins in the food.