Who is Hannah and Morty from Portnoy's Complaint and what is their importance?

Hannah is Alex's sister, essentially portrayed by him as an overweight non-entity. Occasionally she makes an important appearance in the narrative (or rather Alex's memory), but for the most part she is a background character in the drama of his childhood and adulthood. Morty is the man Hannah grew up to marry, a liberal whose politics and views on social activism infuriate Alex and Hannah's father but inspire Alex to follow through on his own socially liberal beliefs.