I have adopted two strays, one who was on her own for at least 4 months and had to fight off Toms at the feeding stations for food. She has a huge eating issue, and will eat anything she can and trust me, she gets plenty to eat and quality cat food so it is not hunger or a lacking of anything in her diet, the other has some eating issues but not as severe.
I asked my vet about this and she stated that once a cat has been very hungry, they have a tendency to have eating issues. Even though your Freda was a skilled hunter, she may have been extremely hungry at times, could even extend back to her kitten days (large litter, not enough food, mom not producing enough milk, etc).
I fostered this
eater with her 7 kittens before I adopted her. As the kittens got bigger, there was huge fighting for a nipple, to the point that I thought they were going to tear each other's eyes out. The smallest of the kittens, who normally lost their nipple to the bigger ones acted exactly the same as Freda (I had them for 5 months, until they were big enough to spay).
As for Elvis, he was young when you got him and he may have picked up habits from Freda.
In saying that, my vote is personality, so some consistent training, with very precise, regular feedings may be needed. If you have a quality raw diet recipe, I think that is better than any cat food you can buy.