Thomas Borthwick is not mentioned in The Scots Peerage account of the family of Borthwick, Lord Borthwick http://archive.org/stream/scotspeeragefoun02pauluoft#page/94/mode/1up or in Stirnet's report on the Borthwick family https://www.stirnet.com/genie/data/british/bb4fz/borthwick1.php
Can anyone provide a source reference that identifies him as the son of Thomas Borthwick and Margaret Sinclair?
