Were the Henderson-Simmonses American or Canadian?

I have not been able to find naturalization records for any, and the evidence available points in conflicting directions. One by one:

Montraville Simmons, Sr. — Despite what the 1910 census enumerator recorded, Montraville was certainly born in the U.S. to American parents. It is also likely that he “immigrated” back into the U.S. long before 1895, and it is not clear why he would have naturalized, unless he renounced his citizenship as a young man. (Canada was a British colony until 1867.)

Anna Henderson Simmons — As the evidence consistently reflects, Anna was born in NC. She was American. Her obituary stated: “Mrs. Simmons was … born in North Carolina. For fifteen years she lived in Canada, where her five children were born.” That is likely inaccurate.

Elizabeth Simmons — This daughter only appears in the 1881 Canada census. She was born about the same time as daughter Moncy and, though the names are not the least similar, may in fact be the same person.

Moncy Simmons Bassett Palmer — Moncy is not listed in the 1881 Canada census in which Elizabeth appears. In U.S. censuses, her birth place is generally consistent, with 1910 as an exception. She provided no information about immigration or naturalization to censustakers.

Doctor T. Simmons — Dock was born in Ontario and consistently provided Canada as his birthplace in records. However, there is conflict about when he immigrated, and neither 1874 nor 1880 seems accurate. If he naturalized in 1917, where is the record?

Susan Simmons Bassett — Susie consistently is described as U.S.-born.

Montraville Simmons, Jr. — Montraville Jr. was also born in Ontario.

James R. Simmons — This son only appears in the 1900 census, was born about the same time as Edward, and was probably, in fact, Edward.

Edward R. Simmons — Edward was also born in Ontario. His World War I draft registration card notes that he gained citizenship when his father was naturalized before Ed turned 21. The 1930 census states that he immigrated in 1900, but that is surely wrong. His obituary says that he lived in Kokomo from the time he was seven years old, which implies that he arrived in the U.S. about 1890.