So glad to hear the little boy is doing better
The raw meat diet can sometimes bring out the cat's prey/hunting instincts, this may be why your little girl has started attacking. It may be worth feeding them in two separate rooms for now.
Fantastic that they liked the meat! Sometimes they can get a bit finicky about the organs - it may help if you cut them very, very finely so that it covers the pieces of meat rather than being a chunk on its own.
When you buy meat, try to find meat with as much fat on as possible - the cheaper cuts of meat are better for cats, for example chicken legs with the skin on are better than chicken breast with no skin.
You're so lucky you've found heart - it's the best meat to feed (it's not counted as an organ so you can feed as much as you like of it) because it contains so much taurine, which is essential for the cats.
Next to do is to get them to eat bones, because this gives them calcium that they need to grow their own bones.. I wouldn't let them go more than two weeks without eating bones. Get a tiny chicken wing and let them have a go
You may need to cut into it a little, or bash it up for them at first. If they don't understand what to do with it, just keep trying every day. They'll get there in the end! Meanwhile, you can add a tiny bit of finely ground eggshells to their food - this will provide the calcium they need until they start eating the bones.
Good luck and I look forward to those pictures!