There are English surnames, Walwyn, Walvin, et al., which derive from an Old English given name, Wealdwine (?), which is made up of Old English words meaning "power" and "friend". The question is - was there a German word for friend like the Anglo-Saxon WIN? I note that there is a German surname, Wallewein, which could be the forerunner of Wellwein. Re the possible French origin, the people of Alsace usually have German surnames.