Earlier Chalmers
The parents of May Chalmers , born Bellie, were definitely Alexander Chalmers, post master & Katherine Anderson.
Alexander Chalmers marries Katherine Anderson on 19/2/1768 in Bellie: they had Helen 1769 & George 1773 in Bellie - but then did they move over 200 km to Perth??? , where the only births of a Mary to an Alexander took place in 1778 & 1780; I do not think so- she claims a 1774 birth of Bellie!
Ancestry trees have her parents as
William Chalmers 23/2/1754 Alvah parish -13/2/1825 Aberdour parish m.20/8/1785 in Alvah Katherine Douglas 1752-
William & Katherine had 11 children 1780-1800
1780. This different May Chalmers was born to William Chalmers & Katherine Douglas on 11/2/1780 at Muiryhill, Alvah parish, Banff- but this 5 years prior to their marriage!!