My father, Joseph R. Dorlaque, son of Joseph Dorlaque, grandson of Antoine Dorlaque (nicknamed "Old Judge" and the inspiration for the now-defunct brand of Old Judge coffee) told me once that Dorlaques and Dorlacs were really all the same family but he had no explanation about the change in spelling. I clearly remember we were directly descended from Francois X.
Sadly, the geneology chart my grandfather had has been lost for many years but went back perhaps 12 generations. Here is what I remember of it: Dorlaques came from the Southern part of France, from a long-gone town called "Orlac". There are Spanish and Spanish Basques are in the line as well. (other surnames from the earliest part of the tree included "du Cadillac", "Barada" and "deMilano")
The Dorlaques were among the first French to settle in Canada, in Arcadia, and fled South when the British attacked, following the Mississippi River into the United States, stopping in the St. Charles area of Missouri unlike the rest of the party that continued on to become "Cajuns" (a corruption of "Arcadaian", making new homes alongside the French and Creoles who had already established themselves in New Orleans.
I have never really tried to substantiate any of this, but if it's helpful to you then I'm glad.