Thomas: Thank you for your message and your continued research.
I was interested in your theory about Duncan and Milton's being the sons of George Thomas Flewelling.
However, there may be a problem with this theory, in that Milton Frederick Flewelling was born on May 6, 1852 (not 1862).That would have made Milton born about 16 months before George Thomas Flewelling and Mary Owens McKeil were married.
Could George Thomas Flewelling have been married before and his first wife died?Could Milton have been born before the 1854 wedding?Certainly all possibilities.
By the way, with your help, I've identified numerous sources and records over in Digby and Annapolis Counties in Nova Scotia that are allowing me to begin piecing together the Letteney family.It appears that, as you conjectured, that most, if not all, these family members indeed were descendants of William H. Letteney, the Loyalist.It's one of those rare families whose name and spelling is generally unique and whose numbers appear to be few (versus my family, which includes Giles, Carter, etc.).