My wife is descended from Euphemia Drummond, sister of botanists James and Thomas Drummond (both of whom have biographies on Wikipedia). I note Euphemia is listed on the FamilySearch tree mentioned. She is buried at Inverarity, sharing a memorial with her daughter and son-in-law. I've seen the book about James Drummond and his house Hawthornden in W Australia. The book provides no evidence, other than family tradition, of a link to the Drummonds of Hawthornden (Midlothian, family mausoleum in Lasswade).
From the other end, I've looked at genealogical information about the Drummonds of Hawthornden (whose separation from the Drummond Castle Drummonds was way back, 1300s/1400s, I think). The family boasts the poet Drummond of Hawthornden active c1650, whose fame would make for an attractive genealogical connection. However, I could not find any convincing line leading to the Inverarity Drummonds. Indeed the Hawthornden lairdship died out in the male line, though the husband of the inheriting daughter took the name and title.
The FamilySearch tree mentioned claims parents and grandparents for Thomas sr, but I don't have access to any supporting evidence or documentation. The claimed grandfather, also Thomas Drummond, married in Edinburgh in 1706, which would provide a possible link to Hawthornden, if valid.
There is Forfar Botanists garden in the town, which marks the lives and achievements of James and Thomas Drummond, as well as of a gardener named Don (ancestor of BBC gardening presenter Monty Don). It features some of the many plants named in their honour.