I have done the family search back to early 1700s with supposition back to 1600s. They are the Dun/Aberlemno/Arbroath/Dundee line but trying to link in the Montrose Berties and the Lochlee (not to be confused with Lochee, Dundee district). I have a lot of incidental information so may be able to help. Working with;
Dr David Bertie (Scottish)
Ian Bertie - One Name Study (English)
Evelyn Bertie