Combining the information from Scotland's People and the IGI produces two lists of children to Robert Mackenzie and Mary Devine
In Aberdeen
Daniel 1847
William 1848
Helen 1850
Christine 1854
Alexandrina 1855
Robert 1858
David 1861
The pre-1855 ones are Roman Catholic baptisms
and in Glasgow
Margaret 1856
Mary 1859
Isaac 1863
The 1871 census has a record of a family at an encampment in Cadder, consisting of Bridget Townsley, widow, 74, born Ireland, with sons Robert, 42 and Isaac, 34, both travelling tinsmiths; daughters-in-law Mary, 31 and Jessie, 37; and grandchildren John, 14; Alexander, 12; Mary, 10, Agnes, 8; Robert, 0; Mary, 12; and Isaac, 8, all surnamed McKenzie. Birthplaces all over Scotland including Glasgow.
In the same census, in Aberdeen, are Robert McKenzie, 42, iron moulder; wife Agnes, 36; daughter Alexandrina, 15 and son David, 9; all born Aberdeen. Mary Ann Devine or Mckenzie, aged 36, died in Aberdeen in 1863, mother's maiden surname Cameron. The 1861 census records that she was born in Peterhead.
So there were indeed two different Robert M(a)ckenzies married to two different Mary Ann Devines.