Were these Johns both with the Macdonalds of Largie?
The classic "Clan Donald" book by Rev. Angus MacDonald (Minister of Killearnan) and the Rev. Archibald MacDonald (Minister of Kiltarlity) mentions both John XII and XIII on page 385 (in a section on the Macdonalds of Largie)
Quote:
XII. JOHN. In 1712 a summons was issued against him by his uncle by marriage, Rev. Angus Macdonald, minister of South Uist, to have himself served heir to his father and his uncle Archibald. We are not informed as to the issue, or whether the service was duly executed. John, 12th of Largie, died in 1729. He was succeeded by his son,
XIII. JOHN, who was served heir to his father on 17th January, 1730. He married Elizabeth, only daughter of John Macleod of Muiravonside, by whom he had one daughter, also named Elizabeth. On 3rd April, 1763, he executed a Deed of Entail, by which his estates devolved upon heirs general. John Macdonald of Largie died in 1768, and was succeeded in terms of her father's disposition by his daughter,
XIV. ELIZABETH. In 1784 she succeeded her uncle, Alexander Macleod of Muiravonside, as heiress of his estates. On 17th August, 1762, she married Charles Lockhart, third son of Lockhart of Carnwath, with issue.