I’m in a similar situation. Have you tried separating your cats for meal times? I shut my thin cat in the bathroom so she can eat her fill in peace, and pick up and put away any food she doesn’t finish. My compulsive-overeater cat doesn’t have the opportunity to poach any more, and he lost the weight he needed to.
I have three cats, all siblings. One of them, S, is fat and will push the others out of the way to get their food. Y will push his sister out of the way but not his bigger brother S. T is a smaller female who gets pushed away by the two others.
At meal time, I throw the bits of kibbles one by one. Those meant for S get thrown far. Those meant for Y get thrown in the opposite direction. Those meant for T are thrown closest. It may seem like work but it’s just another way of playing with your cats. It allows you to regulate how much food they get.
Or you can instill the habit that one of the cats gets fed at one location while another cat is fed at another location, even if they’re close to each other.
Somehow the only place Mojo will not steal food from is his sister’s food dish. Kaia is a grazer, the first dog I’ve ever had that was, and there is almost always food in her bowl but he won’t touch it.
The cutest thing though, when she is in a generous mood she’ll take a mouthful of food from her bowl and drop it on the floor so he can eat it. Even the other dog is trying to keep him fat 
I have no idea how we managed this btw, he’s resistant to almost all training and I still need to keep food off the counters so he won’t steal from us but even when I’m late getting home and his dinner is delayed he leaves her food alone.
I could be a lot more diligent about picking up skinny’s feed bowl after she’s done, but I tend to forget (and there’s the whole laziness thing). I keep imagining that I can make a box with a cut-out that only the skinny one can fit through (but the laziness thing again).
Switching my cat to canned food only worked for me. She went from 16 lbs. to 12 lbs. in about 2 years. I give her ~2 ounces in the morning, and another ~2 ounces in the evening.
One thing that helps me visualize portions without weighing them out is to approximate the size of a mouse. She gets two mouse-size portions a day.
I have multiple cats (OK, 3 of them) and I have to feed them all separately. Not only for weight loss reasons, but also because it is obvious if one goes off their food and this way it is easy to keep the dog from eating all the cat food. Like any routine, it took a few days for the cats to get used to it. I use the bedrooms and my office so I can close doors.
The size of European mice or African mice?
^ Snerk.
Tikva is not happy with the three small feedings a day thing. She’s still waking me up demanding to know where the rest of her food is.
One problem is that the pet feeder is, well, not exactly the best design ever. If you bump it, food comes out. If you move it, food comes out. If you turn it around to check the settings, food comes out.
Eh, we’re dealing.
Has Tivka figured that out yet? 
Heh. 
I’ve laughed in the faces of two different vets who suggested I should play with the fat cats so they get exercise. Pierre lies on his back with his paws in the air, gently wafting them back and forth, if you dangle a cat toy over him. He will pounce ONCE on a dangled string, and if it moves more than six inches away from him, he just loses interest. His life partner Scrappy has a camel hump of fat between his shoulder blades and a gooshy pot belly, and the most exertion he is interested in performing is hopping to the top of the cat perch to sleep in the sun.
Have you had her thyroid levels tested? Old cats commonly develop hyperthyroidism, which will drastically reduce weight. Is she still eating?
I’ve heard this about Fancy Feast, time and again. My cats were mostly larger than they should’ve been, but they all ate Fancy Feast, (or Friskies Buffet before that) and they all except one, lived to be at least eighteen and one made it to twenty-one.
The one exception died of peritonitis at twelve, and he was the thinnest cat among the seven that I’ve had.
I don’t see anything wrong with store brand.
Thats amazing. I’m honestly gobsmacked. It might be because all of the cats I’ve had ate crappy diets before I got them, so their health wasn’t good. I was able to turn them around by changing their diets, but I’ve never had a 21 year old cat. Hat off to you.
Growing up we had a bunch of cats and every one of them ate Friskies, Cat Chow, and sometimes whatever was on sale at the grocery store. The only one of them that didn’t live to old age was killed by a car at the age of about 2 (yes, we used to let them outside - stopped after that). The oldest was a few months shy of 22 when she shuffled off - my parents got her shortly after I was born and she died while I was away at university.
Some were fat, some were thin, but none of them ever had health problems attributed to the food they ate.
Your cat is cute!
Here’s an odd thing: I have never had a fat cat, and I’ve always free-fed my cats.
I have friends who always have fat cats, and they feed their cats on a strict schedule and actually weigh the food.
I don’t understand this at all.
I’m talking 30 years of cats here. Actually, if you add the two households together I guess you could say 60 years of cats.
Hilarity, usually cats can be free fed and not become obese.
But some cats cannot do that, they’ll eat whatever is in front of them. OTOH, it is possible that with the strict schedule, they’re actually feeding more than what the cat needs.
Abbey-cat is 21, senile, blind, scrawny, survived a house fire that killed her companion cat and still is muddling along. She gets some dry crunchies from friskies, and some gushy stuff from fancy feast. We had to have her shaved as she got something nasty in her fur and we couldn’t comb it out. She was never a large or fat cat, her kidneys test out fine for a kitteh her age, her thyroid is a little shot so my brother gives her meds for it.
