Did James Douglas's wife have a slave half-brother and -sister?

[William Douglas]

following receipt of two envelopes, I am currently, amongst other areas of research, looking at the Douglas families of Prince Edward Island, and have come across the following entry:

"Later that year, in Nov 1802, another private sale was recorded that indicates the market value of a young mixed race slave. The conveyance was from "Thomas Hassard Esq. of Charlotte Town" to his son, "William Hassard of lot #49" in repsect of "a certain Mollatta Boy of three years of age called Simon with all his wearing aparrel". Old "Virginia " Tom Haszard had been a large landholder at Boston Neck, Rhode Island, who fought for the British during the American Revolution and who's property was confiscated by the Americans. He settled on the Island of St. John in 1785, and made two conveyances of Slaves before his death in 1804.

William Haszard bargained to pay his father 20 pounds Halifax currency for Simon, who may have been born to a female slave of the elder Haszard. A girl who was given to William's daughters Harriett and Louisa at the same time may have been Simon's sister: she is "one Molatta Girl about five years of age, named Catherine," the title to whom was warranted "against any Claim or Demand Whatsoever"." - From Black Islanders, Jim Hornby, Institute of Island Studies, 1991, IBSN 0-919013-14-7

Simon and Catherine may have been half-brother/sister to Waitsill Haszard, who married James Douglas, controller of customs on St John’s (Prince Edward) Island.

Has anyone got any Prince Edward Island connections?