I believe I have found a link from William Grant's wife, Catherine Grant (maiden name) to the "Second Grants of Wester Elchies" (as described by William Fraser). The 1844 obituary for their son Lachlan states:
DIED -- At Rinnachat, Aberlour, on the 19th Instant, Lieutenant LACHLAN GRANT of the Royal Navy, late of Constitution Hill, Antigua. He was the fourth descendant of Patrick, progenitor of the family of Wester Elchies, second son of James Earl of Moray, by Lady Anne Gordon, daughter of the Marquis of Huntley -- Anno 1663 -- The Lieut. has left a widow, an only son, and two daughters.
More info at http://sensato.com/yabb/YaBB.pl?num=1153228363