These various spellings are all used interchangeably in a few German villages including Hille (near Minden) and in Erkeln. Early records seemed to use Duwel most frequently, and more modern records used Dufel more often, with Duvel used throughout.
In Germany the u would have an umlaut or a ue would be used. Sometimes the name would be spelled with two l's.
In America there are relatively small groups of Dufel, Duvel, Duwel, Duevel, and Duwel, and it is possible we are all part of the same family.
I have researched all of the Dufel families in America and I have contacted many Dufel's in Germany, and would like to learn if any of the families with other spellings have a common ancestry.