The cops had several options they could have chose which would have been legal and not violated “procedures” . They choose the dumbest one, the one most likely to result in violence and mayhem. But hey, two dead middle age people with no priors is just A-OK cuz they “followed procedures.”
Come on now, any other way would have robbed them of their chance to play Rambo.
I'd say when the pit bull started attacking, they no other option to be shoot it. And, that was likely going to happen no matter. I doubt very seriously if either one of the two at the home were going to have a peaceful chat with the officers.