In ancestry.com, the surnames Fleck and Wilt only have the German origins posted, but they do have an English or Irish origin which it doesn't give. Perhaps you are looking for the English origins of the surname Fleck and Wilt, because all 4 of the surnames Fleck, Wilt, Prevost, and Rowland you are looking for are English surnames.
The surnames Fleak and Fleek are defined in ancestry.com, saying both are English surnames, but of unexplained origin. The English surnames Fleek and Fleak are probably variants of the English/Scottish/Irish surname Fleck, found mostly in county Northumberland of England, and coastal counties of West Scotland and Northern Ireland, Northern Ireland being most concentrated. I think this surname Fleck ultimately originated from Northern Ireland, in the county of Antrim where there were many Fleck families living. The origin and meaning behind Fleck, I have no clue.
Now there is the English surname Flick, similar spelling to Fleck, but this English surname Flick is most concentrated in London and East Anglia, mostly in county Essex. A possibility that some Fleck families in America have their ancestors from London or East Anglia, a variant spelling. The surname Flack is also mostly found in East Anglia and London, perhaps a connection between the surname Flick and Flack. The origins are given in http://www.ancestry.com/name-origin?surname=Flack
The surname Wilt is also found in England, but a rare surname, mostly found in Hampshire, Southern England. Perhaps it is a variant of the name Walt, a shorten form of Walter. The origins of Walter can be found here - http://www.ancestry.com/name-origin?surname=Walter