If the female is trying to get pregnant with a male dog then it will go on the males back but if the female dog is going on the males back while pregnant then it may means that they wanted to have another baby.
NO
He will try to mate with her, stand up on her back & hump her. If she is not fixed she will get pregnant.
By mating with a male dog.
No
Sometimes.
Females get spayed, males get neutered.
doggy style. How did you think they do it?
Yes.
Often, a male dog is protective of the pregnant female dog, usually if he is the "mate." Sometimes dogs, mates of the pregnant dog or not, will act aggressivley towards the female dog, also known as the "bitch."
She could die.
No
If the male has not been neutered and/or the female has not been spayed, then yes. And unneutered dog can get any unspayed female dog pregnant.