I put them both in the same category.

Thieving. Lying. Criminals.

Rob Roy would have spoken pure Gaelic. Unless he was wheedling his way out of a tricky sitch via the English.

Did Rob Roy speak Gaelic?HIGHLANDS AND LOWLANDS

Lowlanders spoke Scots, for example, a blend of English and Gaelic with French influences, which Sir Walter Scott and the authors who followed him reproduced in a stylized form in their novels; Highlanders might speak Scots (as Rob Roy does in Scott’s novel) but would also speak pure Gaelic.

Why write his letters in very well “spelled” English?

See from 4:34 in the video below.

We have the same shit that went on here a few years ago. My boys’ remaing grandparents were going to transfer all property and funds into their grand-childrens’ names to avoid some massive loss. Until gov.uk.org got wise and stopped that kind of shenanigans.