Two of my cats are over grooming and losing hair

Hi I have a total of 5 cats, all of which are healthy, spayed, vet checked and up to date BUT... two of my older cats who are sisters, both 8 years old, have been losing an alarming amount of hair on their bodies for the past 2 months. In Florida the winter is considerably drier than the summer so I'm hoping it's just the weather change that's affecting them... none of my other cats are having skin problems, just the two sisters... so Its not mange or anything contagious.. anyone have any ideas or input? Can't take them to the vet arm

Thanks!

Just to be clear, they are over grooming, hence the hair loss. They also are scabby in the areas where they're losing hair, presumably from the over grooming

What are they eating? Could be a food allergy. Could just be dryness, are you using a humidifier/giving fish oil?