Hi there. Just to clear up exactly who Archibald McMillan and Donald McMillan of Taychroman/Tayinloan in Killean were.
Archibald and Donald's parents were Alexander McMillan (b.abt 1757 d.1832) and Margaret Carmichael (b.1762 d.1840) both buried Killean graveyard.
Archibald never married but Donald married a much younger Jane (Jean) McGill in 1846 and they had a large family.
They still appear on the 1871 Scottish census before moving to Ontario, Canada shortly afterwards.
Donald died 20 Feb 1879 in Dunwich, Elgin County, Ontario and Archibald died 10 Jan 1881 in Dunwich, Elgin County, Ontario.