Ninian Magruder, to receive "place that was my brother John Magruder's & 300 acres of upper part of Alexandria, plus share Lot #48 in Marlboro Town. 
Ninian Magruder (born 1686, died 1751), married Elizabeth Brewer (born 1690, died 1751) 
Alternatively, a SAR Application gives the marriage date as 10 Aug 1712 in Prince George's County, Maryland.  This would conflict, however, with the births of the earliest children.
1731 Mother's Will
Ninian was named in mother Sarah's 1731 will
Ninian Magruder of Samuel died in 1751.  Some sources give the death as 1 June 1751 in Prince George's County.  He wrote his will on 6 May 1751, and it was probated on 26 June 1751. At his death Alexandria passed to his son James. 
Samuel Magruder 3rd, b. 24 Feb 1708, m. Margaret Jackson, dau of John Jackson and Ruth Beall 
Elizabeth Magruder (1717-1799) m. Benjamin Perry (1710-1771), whose son in turn Erasmus Perry (1760-1826) m. Elizabeth Harding (abt 1747-1823), daughter of Elias Harding and Elizabeth Beall . 
Sarah Magruder, b. 1713.  Named as Sarah Beall in Ninian's will.
↑ 4.04.14.2 The Yearbook American Clan Gregor Society
↑ Sons of the American Revolution Membership Applications, 1889-1970. Louisville, Kentucky: National Society of the Sons of the American Revolution. Microfilm, 508 rolls. SAR Membership Number: 82978 (retrieved from Ancestry.com)
↑ Source: Record for Ninian Magruder. Author: Ancestry.com Title: Public Member Trees Publication: Name: Ancestry.com Operations Inc; Location: Provo, UT, USA; Date: 2006; Repository: www.ancestry.com
↑ is said by FMMB, p. 108 to have married Captain Alexander Beall, however this is inacurrate; Captain Alexander married first Elizabeth Harding, daughter of John and Elizabeth, and then Sarah Ogle.
↑ Yearbook of the American Clan Gregor Society, Volume LVIII, 1974, page 30. http://archives.ubalt.edu/acgs/pdf/1974.pdf. Accessed November 5, 2016. Member 1696 Walker, George W. 808 Haines Ave. Wilmington, Del. 19809 : he the son of George M. Walker and Helen Day; she the daughter of Luther Day and Ann Eliza Lewis; she the daughter of Jeremiah Lewis and Sarah Jane Clagett; she the daughter of John Clagett, Jr. and Sara
Windsor; he the son of John Clagett and Mary Magruder; she the
daughter of Ninian Magruder Jr. and Mary Offutt; he the son of
Ninian Magruder, Sr. and Elizabeth Brewer; he the son of Samuel
Magruder and Sarah Beall; he the son of Alexander the immigrant.
Thank you to Ila Barnett for creating WikiTree profile Magruder-59 through the import of Wrenn.ged on Jan 23, 2013.
Thank you to David Rentschler for creating WikiTree profile Magruder-106 through the import of Mary Mollie Madeline Davis Family Tree.ged on Nov 10, 2013. Click to the Changes page for the details of edits by David and others.
It may be possible to confirm family relationships with Ninian by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Ninian is a boy, or should be, and these birthdates and fathers match, but I just realized that my (personal) notes list a different wife. Let's keep this unmerged until I can make sure I didn't pick the wrong profiles to merge. :)