Hi again Jeanette H,
Further to my message of this morning, I've made some interesting headway on the Janet Brown/Agnes Brown link. As you've pointed out, there is a discrepancy between their ages. Janet was born in 1715. Agnes' father was only born in 1708 and her parents only married in 1731. Agnes was born in 1732. I think it exceedingly unlikely they were sisters.
However, they could well have been related. The only Janet Brown baptised in the whole of Ayrshire (according to surviving records) in 1715 was baptised in Kirkoswald - where Agnes Brown's family was from. This Janet Brown's parents were Samuel Brown and Agnes Logie. They had married in 1713.
If Janet Brown and Alexander Hutchison used the old Scottish naming convention whereby the first male child was named after the maternal grandfather and the first female child after the maternal grandmother, we can work out that Janet's parents would have been named Samuel Brown and Agnes. So, this fits quite nicely, both date-wise and name-wise.
However, Kirkoswald's records only date from 1694 and I have been unable to work out whether Samuel Brown was perhaps a brother to Agnes Brown's grandfather (or similar).
I had almost given up, until I found a reference in Scotland's National Library to the Cowie Collection - a famed collection of Burns manuscripts. Among the collection is the following reference: "the marriage contract of Samuel Brown and Agnes Logie, 1713". I can only assume Charles Cowie knew of the relationship....
Hope to hear from you soon.
Sean