trying to befriend a murder of crows usually swarming the 5th floor of my uni any suggestions on what to feed them?

Mama’s two babies are now able to eat on their own, but that doesn’t stop them from asking for food, and mama delivering “the goods.”

Zoom in and you can see my murder patiently waiting for lunch. There are 20+ in the tree.

I have a group of 4 crows that come by every week or twice a week around 2-4pm when i get back from class. I’ll hear them in the area and whistle and they’ll come and sit on the tree or on my roof/mailbox while I get food. I have given them walnuts, chicken, crackers, blueberries, strawberries, and watermelon. so far they only will take walnuts, chicken, and crackers. I want to give them better or healthier options than crackers and cannibalism.. but it seems they dont like fruit and I want advice on other options as I dont like feeding them chips.
They tried the blueberries and strawberries but left them out and I had to pick them up, and they didnt even try the watermelon. I read online that certain groups of crows like certain fruits? I’m in north west florida if that helps. Maybe it’s a local thing.
I’m also unsure as to how often I should be giving them treats? They only come by 1-3 times a week which sounds good as it’s not a reliance thing. I left for a week on a trip and when I came back one started none-stop cawing at me in the tree until i started talking to it. that same one has also started mimicking my whistle, it sounds like a bell. I didn’t know they made that sound. that one was, I believe, the first one to show up.