Small note, peacock refers to the male. Peahen refers to the female. Peafowl refers to either gender
Cruelty would depend on the situation.
Out where I live, one of my neighbors raises emus on his property (has a business for it). There are also plenty of cattle, horses, turkey and chickens.
As far as diet, peafowl would do fine. They’re omnivorous, they’ll eat grains, berries, bugs, reptiles. As far as weather, I believe they can acclimate fairly well to Californian weather (of course depending on how north/south and inland you are).
The big question in the cruelty factor is the backyard. I’ve got a 4-acre yard, most of my neighbors have near that if not more. But I know just 2 miles down the road is typical suburbia with a backyard even a dachsund would get bored with.
Legality? I doubt they’re illegal. Even if they are, who’s gonna report you for having peafowl?