Well, after 18yrs of living with the same long haired cat, it's something I'm rarely bothered by anymore 🤪
But I feel you, still. Shedding in pets is like a multi-factorial thing. The "wider" environment (air humidity in home, weather, seasons, etc.), the animal's direct surroundings (mostly food related stuff, but also stressy things like constant noises, human family problems, other animals, etc.), but also the pets themself (age, genetic predisposition, race, allergies, hormonal status, infections, etc.) have an influence. So, finding a reason for "over-shedding" is difficult.
Possible solutions may be: regularly/often used brushes/coombs (with or without vacuum, dry or wet, as gloves or the special kind for thick fur, etc. - whatever works for your cats), food changes (diet for skin/hear health or low on allergens, supplements like (fish) oils, biotin, etc.), a vacuum robot (a lot don't have enough power for pet hairs, but still help to keep the "dirt level" lower), a professional cleaning person (if affordable, especially if needed more than once a week), and, to end my endless blabbing, trying to find a way of coexistence with cat hairs everywhere (and other "legacies" 😉).
I hope you'll find a solution for you and your cats. It probably will take time and cost a lot of nerves, anyway.