EXTREME food obsession/fixation

I have 3 cats, all of which are/were feral rescues. All three are fed twice a day with occasional snacks in the form of treats or appropriate 'human' food snacks (a few chunks of tuna, a tiny piece of unseasoned chicken, etc., all placed in their bowls and NOT given while I myself am eating my meal, in order to not encourage begging behaviors). I am feeding each cat the EXACT amounts recommended by their vet. Before I get into it, here's a bit of context/backstory for each cat:

-The oldest, Persephone, is around 7-8 years old and I found her when she was around 8 months. She does NOT have any major issues with food. Gets appropriately excited around meal time, begs POLITELY during human meal times (She just sits calmly several feet away and stares while we eat.) I can't give her treats unless I lock the kittens up because they will literally take food straight out of her mouth.

-2 kittens, male named Tristan and female named Ona. Siblings, both just over a year old now. I rescued them when they were around 3-5 weeks old and required bottle feeding. When I found them they were extremely malnourished, had a plethora of medical issues, and were honestly not far from being on the brink of death. Ona was much worse off than her brother, as I didn't find her until around 48hrs after I found her brother.

My problem is the kittens. Ona and Tristan both have the most insane and aggressive obsession with any and all food that I have ever seen. Ona will literally snatch food right out of my hand halfway to my mouth if I let my guard down. Locking them in another room while I eat results in yowling and property damage (bye bye security deposit, several doors in my apartment will need to be replaced due to deep gouges and literal chunks bitten off). Both kittens will obsessively try to get to any food within reach, often in a crazed and frenzied state that is more reminiscent of a fully feral animal and not a cat that's been living a cushy and spoiled life since before they even started eating solid food. Not even the food in my cupboards are safe because Tristan has learned how to open not only the cupboards but also the pantry door. I now store all of my bread, tortillas, or any food in soft plastic bags or wrappers/cardboard containers inside of my MICROWAVE because there is no longer any safe place to store them that Tristan can't get into. I give it a few months before he figures out how to open the microwave, too 😂

Feeding time has become this whole insane and chaotic process, and due to the kitten's behavior I have to lock all 3 cats in different rooms while they eat. If I don't separate them, the kittens will literally abandon their bowls to go eat out of the other cats' bowls despite have a whole meal of their own right in front of them! All three cats get the same exact food in pretty similar portions.

I have no idea how to stop this behavior. Persephone was so, SO easy to train! She also had a bit of food obsession the first year or so after being rescued, but once she realized that every meal was a guarantee and there would always be more later, her food obsession just kind of went away on it's own.

But the kittens? I've had them for over a year now and they show no signs of improvement. In fact, I feel like it's getting WORSE with each passing month. They haven't been able to eat around eachother ever since I weaned them and switched to solid food. But separating them each into separate rooms for meals twice a day is chaotic and stressful and honestly kind of exhausting.

Things I've tried to curb this behavior:

-Increasing the portion sizes for each meal

-Clapping loudly and saying no whenever they display the obsessive food behavior (they 100% ignore me, zero effect)

-Spraying 'bitter' cat-repellant spray on the human food containers they can get into (worked for all of 2 days before they stopped caring completely)

-Automatic timed feeders (they destroyed every single one trying to get to the food inside in between feedings)

-More snacks throughout the day (this caused more chaos than it prevented, honestly)

-Tried multiple different brands of cat food (they react the same no matter what food is involved. They get equally feral over fancy wet food as they do over a brick of uncooked ramen noodles)

-Adjusted their feeding schedule many times (Even with FOUR meals per day, no change in behavior)

-Using puzzle feeders and slow feeders (makes them eat slower but gets them so worked up that they become visibly irritated and frustrated, and therefor more destructive)

-Using a spray bottle (This works for Ona, but Tristan could absolutely care less and lowkey seems to enjoy it sometimes.)

-Put child locks on all cupboards AND trash cans (Tristan can and will find a way to chew through or otherwise disable most affordable child lock options. Same with the slow/puzzle feeders, this just causes him to get more destructive in an attempt to get to the food)

-Locking the kittens up while the humans eat (again, this causes more destruction of property and does nothing to curb the behavior itself.)

At this point I'm at my wit's end and have found myself becoming enraged to the point that I recently smacked the ever-living CRAP out of both kittens for literally stealing food straight out of my hand while I'm eating. To me that is NOT okay and I despise the fact that I reacted physically and laid a hand on them in that way at all. (I feel the need to stress that neither kitten was harmed at all, the strikes were to their rump area, and weren't hard enough to do anything more than lightly jostle them... They showed ZERO REACTION and actually became MORE insistant on getting the food. But I still do not condone physically reprimanding a cat like that for any reason at ALL.)

I feel like I've tried everything, yet their behavior hasn't improved in the slightest in over 8 months. My vet basically told me it is what it is, cats will be cats, and even coo'd and aww'd at the video I showed her of the kittens VERY aggressively fighting me to get at an empty bag of cereal I was trying to throw away. Like the behavior is CUTE somehow?!

One thing I've been considering is to try free-feeding? If the food is ALWAYS available, my hope is that over time that "must obtain food at any and all costs" mentality would lessen or disappear entirely. (I should note that none of the cats are aggressive towards eachother or towards us hoomans in any way. No hissing, growling, or that type of physical aggression of ANY kind.) My worry with that though is that the kittens will overeat to the point of physically harming themselves or making themselves sick. They are VERY active so I'm not too worried about weight related problems. I'm willing to try anything at this point, because this behavior has entirely upended me and my rommates' lives. Every feeding time becomes a battle of wits. Every human meal becomes a lesson in creativity and perseverance. Every midnight snack becomes a covert stealth mission.

So here I am begging for any and all advice y'all have to offer. What training methods have you guys had success with? What training methods DIDN'T work? And how did your cats handle going from timed feedings to suddenly being free-fed?