The letter to Robert and Ruth clearly states Isabella McGillivray being in the family. Margaret Scott and Alexander are the parents of John 1st McDonald.
John McDonald (1939- died Nov. 18,1909 Braeside)
Isabella Mcgillivray (1844-1916)
Ranald McDonald (1815-1892) and Penelope(1822-1904)
You are right. Further researh needs to be done. The connection of John 1st to Margaret Scott is accurate.
thank you for steering me in the right firstname.lastname@example.org