1. William Fergusson[e] was one of the witnesses at Lydia's wedding.
2. According to witnesses at Lydia's divorse trial, she had at least one other sister.

John Fergusson (or Ferguson) was descended from the Fergusons of Inverurie, Aberdeenshire - see http://dna.cfsna.net/GEN/Aberdeen/Inverurie.html

David Chudleigh summarizes John Fergusson as follows:

"Captain Fergusson R.N. earned the epithet of “Black Captain of the Forty-five” for his extraordinary cruelty against the supporters of “Bonnie Prince Charlie” in 1745 Rebellion. His men pillaged and burned the properties of all suspected sympathizers. When they arrived at a house, if they found the man of the house present, they passed by. If he was not present they assumed he was off fighting with the rebels and they would steal everything of value from the house, burn it and steal any food or livestock that they found.

In 1758 Fergusson was the captain of HMS Prince of Orange, a 4th rate of 60 guns. He was part of the expedition against Louisbourg in 1758, under the command of Mr. Boscawen. This is intriguing because Jean-Antoine Charry, marquis des Gouttes, who owned Château Riau, near Dornes, France and who would later be the godfather of John Fergusson’s grandson Jean Elisabeth François Georges Newman, was the commandant of the entire French squadron at Louisbourg. In those days high-ranking officers were not imprisoned but were placed in a suitable situation in the country of their opponents. My guess is that he returned to England on the Prince of Orange, and became friends with Captain Fergusson. He may have even been a “guest” in his home. Lydia Fergusson was born the year he was captured. The war ended at the treaty of Paris 10 Feb 1763, so he may have been in England until then. He may have been like an uncle to her which would explain why she might go to him for help when she found herself pregnant, and her very angry husband returning from America!"

David Chudleigh's summary is derived from the Records of the Clan Fergusson which presents a digitized version of an a1895 book titled "Records of the Clan Fergusson or Ferguson" published by the Edinburgh University Press. The transcript contains many errors which have been corrected in the text below as taken from the orginal text available at http://ia700307.us.archive.org/23/items/recordsofclannam00ferg/recordsofclannam00ferg.pdf.

This John [Ferguson] was the 'black captain' of the 'Forty-five' and a most active officer. Several anecdotes of him have been preserved. He is said, on arriving off the coast of Skye, to have got into conversation with a dairymaid from Kingsburgh house, and to have had her shown over his ship, when the girl let out the important secret by saying 'she had seen many nice gentlemen, and the Prince was at her master's house night before last, and was a very nice gentleman, but not half so kind as Captain Ferguson.'

The Jacobite writers describe him as 'a most active emissary of the Hanoverian party' and as 'a fitting tool for William the Cruel.' He more than once narrowly missed capturing the fugitive Prince, who on arrival both at Morar and Boradale found the houses 'burned by Captain Ferguson.' It is recorded as an instance of second sight that the arrival of his ship on the coast of Skye on the hot scent of Prince Charles was foreseen by a Highland seer: it was to that ship that Flora Macdonald was taken on her arrest, and a combined party of sailors from it and Campbell Militia secured only a lesser prize in the seizure of Lord Lovat.

The following notice of Captain John Ferguson is given in Charnock's Biographia Navalis: —

‘This gentleman in the early part of the year 1746 was commander of the Furnace bomb, then employed as a cruiser off the coast of Scotland. (He "seized 800 stand of arms at M'Donald of Barrasdale's house, in the isle of Rasay.") He rendered himself so conspicuous on that station by his activity, diligence, and general conduct, that he was, on 6th October in the same year, promoted, it is said in consequence of the express interference and recommendation of the Duke of Cumberland, to be captain of the Nightingale, a new frigate just then launched. During the ensuing year we believe him to have been principally employed as a cruiser, and in the month, either of September or October, he again distinguished himself by the capture of a French ship of somewhat superior force, called the Dauphin Royal, carrying 22 guns and 150 men. The enemy made a very obstinate though running fight, and was not overpowered till after a contest of ten hours’ continuance. No further mention is made of him till the year 1753, when we find him commanding the Porcupine sloop on the coast of Scotland, and very actively employed in scouring that quarter, and preventing the return of the rebel chiefs, many of whom, after having escaped to France, it was then rumoured, were on the point of attempting to repair again to their native country, in the hope of inciting some fresh insurrection. (He was not long afterwards appointed regulating officer on the same station.)

‘We have no account of him after this time till the year 1758, when he was captain of the Prince of Orange, a fourth-rate of 60 guns, one of the ships sent on the expedition against Louisbourg, under the command of Mr. Boscawen. He remained in the same station during a considerable space of time, but neither himself nor his ship are again noticed till the year 1762, when the Prince of Orange was one of the Channel Fleet under the orders of Sir Edward Hawke and his Royal Highness the late Duke of York.

'In both the services last mentioned, as well as every other in which he was employed during the war, he appears to have unfortunately had no opportunity of increasing either his fame or fortune. After the conclusion of the war he was appointed to the Firme, a fourth-rate of 60 guns, as he afterwards was to the Prince of Orange, a ship of the same force. He died on 13th June 1767.

‘An anecdote is related of this gentleman in Entick's History which we think it would be an act of injustice to him to suppress. The coast in the neighbourhood of Louisburg was so extremely well fortified, both by art and nature, that it was generally deemed almost an impracticability to effect a landing; the admiral took the advice of each captain separately, and, to use the historian's own words: "It coming to the turn of Captain Fergusone, an old, brave, and experienced officer, whom Mr. Boscawen had requested from the lords of the admiralty to attend him in this service, and in whose opinion and conduct in the most trying occasions he could place great confidence, this captain having delivered himself in the most respectful terms in regard to the opinion of his brethren whose reasons the admiral ingenuously related to him, and despising the arguments drawn from the danger of the service, for proving an impracticability without an actual attempt to land, and to force the enemy's forts with all the art and strength in their power, he advised the admiral for his own honour and the glory of his country to exert that power with which he was invested, and not to leave it to the uncertain resolutions of a council of war, which had been so fatal at Minorca, at Rochfort, and even at Halifax, to the disgrace of all concerned, and to the extreme loss of the nation."

‘The admiral acquiesced in the justness of the captain's observation on councils of war: resolved to call no council, but strictly to adhere to his instructions, which were to land the troops on the island of Cape Breton.'