It would appear from the data on familysearch.org that the Betsey Phinney who married David McLellan is most likely the daughter of Edmund Phinney and Sarah Hamblin, or possibly the dau of Stephen Phinney and Anna Huston. In either case, these 2 men are sons Edmond Phinney of Barnstable, MA and Elisabeth Meserve.
US Census, 1850 Cumberland, Cumberland, ME
David Mclellen M 64 ME abt 1786
Betsey Mclellen F 63 ME abt 1787
Maine, Births and Christenings
Betsey Phinney
Birth 01 May 1787 Gorham, Cumberland, ME
Father Edmund Phinney
Mother Sarah Hamblen
Edmund Phinney
Birth 26 Nov 1760 Gorham, Cumberland, ME
Father Edmund Phinney Mother Betty Meserve
Sarah Hamblen
Birth 07 Dec 1759 Gorham, Cumberland, ME
Vs. Birth 17 Dec 1761 Gorham, Maine
Father Joseph Hamblen Mother Hannah Whitney
Stephen Phinney
Birth 10 Mar 1763 Gorham, Cumberland, ME
Father Edmund Phinney
Mother: Betty Meserve
Maine, Marriages
Groom Stephen Phinney
Bride Ann Huston
Marriage 09 May 1788
Betsey Phinney
Birth 05 Jun 1789 Gorham, Cumberland, ME
Father Stephen Phinney Mother Anna Huston
From: DAR.org
Edmund Phinney Jr born on 26 - Nov - 1760 at Gorham ME died at Harrison ME on 18 - Jun - 1828 and his ( 1st ) wife Sarah Hamblen born on 7 - Dec - 1759 at Buxton ME died at Harrison ME on 15 - Feb - 1833 married on 26 - Mar – 1780.
The Said Edmund Phinney was the child of Edmund Phinney born on 27 - Jul - 1723 at Barnstable MA died at Gorham ME on 15 - Dec - 1808 and his ( 1st ) wife Elizabeth Meserve born on 2 - Sep - 1730 at Scarboro ME died at Gorham ME on 6 - Aug - 1795 married on - - 1750.
PHINNEY, EDMUND Ancestor #: A090859
Service: MASSACHUSETTS Rank(s): COLONEL, CIVIL SERVICE, PATRIOTIC SERVICE
Birth: 27 Jul 1723 BARNSTABLE MASSACHUSETTS
Death: 15 Dec 1808 GORHAM ME DIST MASSACHUSETTS
Service Description:
1) DEL TO PROV CONG; SELECTMAN
2) REP TO GEN COURT, 1778-9
Spouse: Elizabeth Meserve