Dog Has Forgotten How To Be Dog?

My sister is staying with me. She adopted her dog from another family in November he is 5 years old. He is a lab x greyhound and was spending 12-18 hours a day crated (24 hour day).
My two dogs are very use to being in a regular pack and having all kinds of animals in the house.
My sister’s dog seems to have forgotten how to be a dog. He’s OBSESSED with balls, he “gives paw” ALL THE TIME, he’s not well trained, he’s not really good around his food, but all other behaviours are submissive to ALL humans. He still drools around the cats and whines, he’s been here for 6 weeks now. He demands attention, even shakes when he doesn’t get it.
I’ve been trying a lot of things with him, I’m very inspired by Caesar Milan personally. He now is ok with my little dog, but still only so so with my big dog.
Suggestions?
yes, they were introduced over time and getting use to being in each other’s houses before they came to live here. he is fairly well exercised.