The McMillans on the Census

My Great grandfathers family - The McMillans .....

1891 Census – William McMillan and family living at 2 Clyde Row, Blantyre
William McMillan, age 53
Jane McMillan, age 53
John and Jane would be 25 and 22 – probably left home
Catherine McMillan, age 21
William McMillan, age 17
Samuel McMillan, age 15
David McMillan, age 12 (my great grandfather)

1881 Census – William McMillan and family living at Garden Terrace, Blantyre
William McMillan, age 46 – born in Ireland circa 1835
Jane McMillan, age 45 – born in Ireland circa 1836
John McMillan, age 15 – born in Ireland circa 1866
Jane McMillan, age 12 – born in Ireland circa 1869
William and Jane left Ireland between Jane and Catherine being born 1869-1871
Catherine McMillan, age 10 – born in Blantyre, Lanark circa 1871
William McMillan, age 8 – born in Blantyre, Lanark circa 1873
Samuel McMillan, age 6 – born in Blantyre, Lanark circa 1875
David McMillan, age 3 – born in Blantyre, Lanark circa 1878/9 (my great grandfather)

Could not find William and Jane McMillan on the 1871 Census which might mean they arrived in Scotland after the Census was taken/after the birth of Catherine in 1871.