I always imagined a young version of Jimmy Smits as Ranger, and the late Estelle Getty as Grandma.
For some reason, Robert De Nero came to mind with Stephanie's father.
For Stephanie herself I always pictured Debra "Will & Grace" Messing.
No idea for Morelli.
No idea for the mother, but contrary to his description in the books as tall, thin, and weaselly, I always picture Danny De Vito as Vinnie.
I saw an episode of My Name Is Earl, and there was an actress who played Crabman's sister, and she would have been perfect for Lula. Not sure of her name, though I think this might be her.
http://images.wikia.com/mynameisearl/im ... Turner.jpg