Generally the alpha pair are the only two that breed. A small percentage of packs will sometimes have Beta males, who will also breed with the alpha female. Beta males generally occur when two brothers disperse from the same home pack as two or three year olds and travel in search of a female, and a female accepts both males. Yearling females or sub-adults may go through a false cycle when the alpha female becomes pregnant and may become a wet nurse to her new siblings. The entire pack is involved in the raising of the pups.
Prolactin is present in each member of the pack, male and female.
Some will stay with their original packs for life, and just be part of the pack. Those that choose to not leave or disperse will typically not give birth or raise young of their own. Packs are very territorial and will even fight to the death to protect their territory. We have seen the surviving alpha's traveling with several offspring, and often siblings will travel in groups as well. We have even observed all surviving pack members sticking together with the surviving alpha locating a new mate.