Am not related. There are numerous posts for Jehiel Beardsley Hathaway at Rootsweb World Connect. typical;
Father: Benjamin Hathaway b: 28 MAR 1747 in Freetown, Bristol, Massachusetts
Mother: Elizabeth French b: 14 JUL 1768 in Berkley, Massachusetts
In one of the DBs Jehiel is listed as one of 13 children. Assuming Elizabeth was his mother, she would have been about 43 when he was born; reasonable age. None of the DB's indicate an alternate marriage. Also found no indication of a Beardsley "legacy name".
Have you contacted anyone posting to the Rootsweb World Connect for insights/sources? You also might try the Hathaway Family Association website http://www.hathawayfamilyassociation.org/