Martha Avery was not the mother of Pelatiah Bliss' children. She was married to Peter Comstock and was the mother of his children, whose were born in the same time frame as the children of Pelatiah Bliss. She married Pelatiah after Peter's death. Look for the Comstock family history, which backs me up on this.
So, Sarah Harris Brown Bliss was the mother of Pelatiah Bliss' children.