My theory is that either the Triton’s move either during the time he was a baby or  ten years before Unwound Future. I got at least two theory’s on why

1.  Since the Triton’s are a rich family, Luke is a little baby and their only form of security is Doland (and how well that turned out), any bad guy can swoop down to his room, kidnapped him from his crib, and threatened them with either you give us all of your money or the baby dies. Brenda, worrying about her sons safety, suggested Misthallery because its a close, safe, rural town.
2. 10 years before unwound future, Luke as a toddler, begins to develop the ability to talk to animals, and no doubt that ability is useful to all kinds of creeps like poachers, and animal extremists (remember Carface from All Dogs go to Heaven when he used this one girl to talk to animals to fix bets), thus they moved to Mistallery to hide themselves from the cruel dark world 

Well, I tried, but I’m terrible at explaining things, because I tend to go all over the place, so yeah