That Catholic marriage is there in the Roman Catholic registers on Scotland's People - Charles has been Latinised as Carolus Grant, married Elspet Miller 25 July 1848 at St Andrew's, Braemar.
And there are two Catholic baptisms - an unnamed child born on 24 and baptised 29 April 1849, and Elspeta, born 3 and baptised 8 December 1850. In both the parents are shown as Caroli Grant and Elspetae Miller.
It's pretty common for given names in Catholic registers to use the Latin form of a name or, if no Latin form actually exists, to invent one.
Charles is from Germanic, from the same root as the archaic English word churl, from which we get churlish as in bad behaviour, but he has a long pedigree as Carolus when Latinised - think of Charlemagne, 13 centuries ago, who was Carolus Magnus in Latin, equivalent to Charles the Great in English.
Elspet has no such pedigree. Originally she was a variant of Elizabeth, and sometime the two names can be used interchangeably, but not always, because you do find families with both an Elizabeth and an Elspet among their daughters. She's easy to Latinise, because all you need to do is tack an a on the end.
If you did Latin at school you'll know already that most male names end in -us, and female ones almost invariably in -a. The -i at the end of a male name and -ae at the end of a female name are the Latin way of saying 'of'. So Caroli Grant means 'of Charles Grant' and 'Elspetae Miller' means 'of Elspet Miller'.
