Yes, sources I've seen show Nathaniel b1671/2 and Nehemiah b1680/1 as sons of Samuel Allen & Sarah Partridge. And with the 1st Nehemiah having a son Nehemiah b1715; but nothing more about the 2nd Nehemiah.
It is certainly possible that Mary Allen b1760 (of Nehemiah & Abiah) could have married twice—I only have one Internet source for her. Haven't seen a Mary b1763 in this family.
Hmmm, wonder where the Nehemiah b~1756 fits in; haven't seen him anywhere in this family either. Lots of guys with the same name sure make it tough to keep them straight. FWIW, here are some of the descendants of Samuel Allen (1598-1669) of Braintree, MA:
1-Samuel Allen (1598-1669) + Ann Whitmore 2-Samuel Allen (1632-1703) m Sarah Partridge 3-Samuel Allen III (1660-1736) m1 Rebeckah Cary 4-Samuel Allen IV 4-Ephraim Allen 4-Timothy Allen 4-Joseph Allen 4-Mehetable Allen 4-son Allen m2 Mary Pratt 4-Joseph Allen 4-Benjamin Allen 4-Mary Allen (b 11 Jun 1704, Bridgewater, MA) m Lt Henry Kingman 4-Rebecca Allen 4-Capt. Matthew Allen 4-Dea. Seth Allen 4-Abigail Allen m3 Jane Vining 3-Essiel Allen (1662/3-1737) 3-Mehitabel Allen (1664/5-1727) m Isaac Alden 3-Sarah Allen (1667-1738) m1 Jonathan Cary; m2 Benjamin Snow 3-Bethia Allen (1669-1743) m John Pryor 3-Nathaniel Allen (1671/2-1751) m Bethia Conant 4-Andrew Allen (b 1698) m Abia Lovell 4-Hannah Allen (b 1700) m Moses Goodspeed 4-James Allen (1704-1778) m Mary Packard 4-Abigail Allen (1710/11-1782) m Nathaniel Carver 4-David Allen (b 1712/3) m Fear Pratt 4-perhaps Mercy Allen (b 1714/15, twin) m Moses Orcutt 4-Mary Allen (b 1714/15, twin) 4-Bethiah Allen (b 1707/8) 4-Hephzibah Allen (1722-<1736) 3-Ebenezer Allen (1674-1730) m Rebeckah Scate/Skeath 4-Sarah Allen 4-Rebecca Allen 4-Jacob Allen 4-Joanna Allen 4-Abigail Allen 4-John Allen 4-Ebenezer Allen 4-Ephraim Allen 4-Isaac Allen 3-Josiah Allen (1676/7-17360 m Mary Read 4-Josiah Allen Jr 4-Mary Allen (b 27 Apr 1714, Bridgewater, MA) 4-Esther Allen 4-Sarah Allen 4-Nathan Allen 4-Bettie Allen 4-William Allen 3-Elisha Allen (1678/9-1720) m Mehitabel Byram 4-Susanna Allen 4-Elisha Allen Jr 4-Japheth Allen 4-Matthew Allen 4-Samuel Allen 3-Nehemiah Allen (1680/1-?) + Sarah Wormel 4-Alice Allen 4-Sarah Allen 4-Martha Allen 4-Nehemiah Allen Jr (b 8 Jul 1715, Bridgewater, MA ) no more 4-Bethiah Allen 3-Joseph Allen (1686-?) 2-Mary Allen (1634-1709) m Nathaniel Greenwood 2-Sarah Allen (1639-1690) m Lt. Josiah Standish m Margaret widow of Edward Lamb 2-James Allen (1737-1714) m Elizabeth Partridge 3-Amy Allen 3-Mary Allen (b 22 Dec 1665, Sandwich, MA) 3-Abigail Allen 3-Ruth Allen 3-Ebenezer Allen 3-James Allen Jr 3-Ichabod Allen 3-Samuel Allen 3-Col. John Allen 3-Lt. Joseph Allen 3-Sarah Allen 3-Rev. Benjamin Allen 2-perhaps Abigail Allen (~1641-1729) m Dea. John Cary Jr 2-Joseph Allen (1650-1727) m Ruth Leeds 3-Joseph Allen (b 1672) 3-Abigail Allen (b 1674) 3-Samuel Allen (b 16760 3-Benjamin Allen (b 1679) m Rebecca 3-Rebecca Allen (b 1681) 3-John Allen (b 1686) 3-Mary Allen (b 1688) m Lydia widow of Samuel Holbrook