Hi from Australia,
The surname Hallac is actually pronounced Hal-latch. Not unlike the surnames Blacksmith and Baker, the surname Hallac comes form an old Turkish trade of fluffing handmade mattresses(as were used in the Byzantine and/or Ottoman eras. So, Hallac = Fluffer , lol I guess it loses a little in translation. But it was quite a well-relied-upon trade. :)
PS Im a relative of yours by marriage. Ask Uncle Ismet ;)