I’m not sure what family information has been handed down but the facts as put forward through the records do not indicate any great family secret. From the 1920 and 1930 US Census there is a widowed Sophia born about 1864 in Canada and her two sons. There is no reason to believe that they aren’t her sons. She is certainly not too old to be their natural mother, both census refer to them as her sons. There are small descrepancies in the ages from the 1920 to the 1930 Census but that is not unusual.
The 1930 Census states that they immigrated in 1902 but chances are they may have travelled back and forth between Maine and Nova Scotia many times before they settled permanently in Maine. People forget just how easy and inexpensive it was to get on a ship just about anywhere along the coast of NS and travel to the New England states
If you check the US Census Record for Danforth, Washington Co., Maine where she is living in 1930, you will find the large family of William and Myrtle Mailman, both born Canada. If you check Nova Scotia Vital Stats you will find the record of Willam Mailman, son of Asaph and Sophia marrying a Myrtle Shipley in 1902, so Sophia was not by herself. She had a son, daughter-in-law and many grandchildren living in the same community. Chances are there were other members of her family living in the area also. I noticed a Crabbe family living in the same area.
As for her daughters Alice married Thomas Milner in Annapolis Co in 1896, Phoebe married Charles Edward Morgan in Digby in 1902, Ellie married Elijah Raymond in Digby in 1909. Can’t seem to find a marriage for Clara but that’s not unusual-a lot of things didn’t get documented in rural Nova Scotia during that period. Clara may have gone to the US also; perhaps married there.
As far as First Nations connections-there doesn't seem to be any reason to think that Edward or George were Mi'kmaq.
The boys are certainly not identified as being anything but “White” and my experience is that American Census-takers were very careful about separating white from non-white citizens.