Good for you to be able to check key details on your direct line. I think you will find the McBays from these areas are well researched and lots of details available online. For this reason, you need to check on Scotlands People and get the key names/dates to help you work back with confidence. There are a numer of researchers here on RootsChat with an interest in McBay from these areas and period, see:
www.rootschat.com/forum/index.php?topic=404371.0www.rootschat.com/forum/index.php?topic=498513.0For James, there is this possible birth indexed herehttps://familysearch.org/ark:/61903/1:1:XY1Z-2HS
If we are correct with the names of James McBay and Isabella Criggie for Edward's parents, there is also this possible data on James:
3 Edward McBay b: 1848 d: 1 Oct 1931
+ Georgina Waiter b: 5 Nov 1853 d: 15 Jan 1937
4 James McBay b: 4 Nov 1872
+ Isabella Criggie b: Abt 1879
5 Georgina Waiter McBay b: 30 Oct 1903
4 Bell Mearns McBay b: 28 Oct 1874 d: 13 Jan 1960
+ James Ritchie b: 31 Dec 1869 d: 28 Mar 1955
4 Edward McBay b: 1 Nov 1876
4 Alexander McBay b: 17 Nov 1878
4 William McBay b: 28 May 1881
4 Margaret Waiter McBay b: 23 Nov 1883
4 John McBay b: 23 Nov 1883
4 Georgina McBay b: 4 Nov 1886 d: 20 Oct 1964
4 Robert Whitby McBay b: 2 Jan 1889
4 Ann Cuthbert McBay b: 1 Dec 1890
+ Joseph Taylor Renny b: 2 May 1891
4 Elizabeth Ann McBay b: 13 Nov 1893
4 Charlotte Taylor McBay b: 19 Jan 1896 d: 20 Sep 1987
http://worldconnect.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=DESC&db=johnstrachantree&id=I906For Isabella Criggie, there is data available to check such as
www.ancestry.se/boards/localities.britisles.scotland.kcd.general/897.1.1.2.1.1.1/mb.ashxMonica