Hi Alan,
Here are the inhabitants of 115 Union St in 1881:
1881
115 Union St, Aberdeen St Nicholas
James Garrow, 57, Head, born Foveran, Aberdeensh, Collector of Customs
Elizabeth Garrow, 61, Wife, born Foveran, Aberdeensh
Jeannie Garrow, 28, Daughter, born Aberdeen, Aberdeensh
James Garrow, 25, Son, born Aberdeen, Aberdeensh, Fishmonger
Robert Garrow, 23, Son, born Aberdeen, Aberdeensh, Fish and Game Dealer
Did the references you found give an occupation for George Cheyne and John M Simpson?
Regards,
Sarah
Later:
I think the John M Simpson you found must be this one... born in Kintore, of course

Must be a relative of some sort. And his wife is Margaret-- another contender for an honorary Aunt Maggie?
1891
Varvill Bank, Aberdeen Old Machar
John M Simpson, 38, Head, born Kintore, Aberdeenshire, Granite Merchant
Margt Simpson, 39, Wife, born St Nicholas, Aberdeeshire
Anne K Simpson, 13, Daur, born Old Machar, Aberdeenshire, Scholar
David B Simpson, 10, Son, born Old Machar, Aberdeenshire, Scholar
Ernest J Simpson, 8, Son, born Old Machar, Aberdeenshire, Scholar
John appears to be this birth on the IGI:
John Milne Simpson
Birth: 14 Aug 1852
Christening: 10 Oct 1852 Kintore, Aberdeen
Father: James Simpson
Mother: Agnes Snowie