Have you found and made any contact with the possible second family for Hugh in the US?
Added: See you have made contact and have been able to compare DNA with the American family which is great to have that confirmation.
...Hughs naturalisation petition says 1854 but that was not right as his DNA was fathering his daughters in Scotland (i match for them and also my cousins, Hughs US decendants)!
Hugh's 1910 US census entry in Minnesota is probably more accurate giving 1866 as the year that Hugh arrived in the US (give or take

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www.familysearch.org/ark:/61903/1:1:M2LK-TDXMonica