That genealogical note about 'our poet' is a bit convoluted!
However I see that the paragraph before the one quoted by MonicaL refers to James Monteath MacCulloch as the poet.
There is a marriage of George McCulloch to Helen Monteath in Dunblane in 1831, and John Monteath married Helen McCulloch in 1824, also in Dunblane.
1851 Census, King Street, Stirling: George McCulloch, 36, printer's clerk, born Lecropt, with wife Helen, 45, and children George, 17; Margaret, 13; James, 10; William, 7; Helen, 5 and Isabella, 3.
So if we're discussing the poet's paternal grandfather he'd be a McCulloch, not a Monteath?
Helen McCulloch, other name Monteath, mother's maiden surname Christie, died in Stirling in 1866, aged 57.
George McCulloch and Margaret Christie had Jean 1802; John, 1803; John, 1804: Isabella, 1805; Margaret, 1812; George, 1814, all baptised in Lecropt. I can't find Helen's baptism.
There are baptisms of children of John Monteath and Helen McCulloch in Dunblane: Margaret, 1825 and Jane 1827; and of children of John Monteath (no mother named), all in Dunblane: James, 1841; Catharine, 1843; Henry, 1845; Mary, 1850; Isabella, 1854. The ones with no mother named match those of Isabella Henderson listed in the census.
In 1841, in Stirling, are Helen Monteath, 30; Jean Monteath, 13; Helen Monteath, 11; Isabella Monteith, 9; and James Monteath, 7. There is another listing of Jean Monteath, 13, a female servant in a household in Stirling. In 1851 there are Helen Monteath, widow, 42, born Dunblane; Margaret Monteath, 25; James Monteath, 17. Both Helens are still in Stirling in 1861, the daughter married with two children, Helen and Margaret Robin.
So it does look as if this is two separate families, one the family of John Monteath, who died before 1851, and Helen McCulloch; and the other, a different John Monteath married to Isabella Henderson.
You need to look at the 1866 death to see if this is Helen McCulloch, widow of John Monteath, and what her husband's occupation was.