Well here is a plausible answer and it does not depend on Non Paternal Events. I looked back at the earliest records we have for Wheatons (& Hancock) in Devon. I have added all possible spellings although some may be totally unrelated. Surprisingly there are no Whiddons which later show up as a prominent family in Chagford. You can see that there are clusters by spelling and locale which may account very the different DNA signatures.

List of Earliest Records

1332 Richard Hanecock Esse Abbatus (Ashford)
1332 Thomas de Whitton, South Molton
1288, 1298, 1302-20 Roger Le Whetene  aka Roger Bevyn le Wheten,  Mayor of  Exeter 
1332 Gilbert le Wetene Exeter
1332 William Wetedene, Abbotskerwell
1332 William Whetene,  Halberton
1376 Alexander Leygh aka Alexander Wheton, Tiverton

1367 John Whetene, Mayor of Dartmouth

1332 Roger atte Wettene, Newton St. Petrock
1332 William Whetena,  Woolfardisworthy
1332 Simeon Wadeyn, Bradworthy

1332 Richard Waddon, Colyton
1332 Roger de Wadetun, Berre Ferrers

1332 Roger de Weydon,  Meshaw
1332 Robert Wytoun South Taunton, (near Widdon Down)
1332 Robert de Wottone, Exeter
1332 Henry de Wooton, Sidbury
1332 William de Wooton, Woodbury
1332 Gilbert De Wottone,  Torbryan with Denbury
1332 Roger de Wottone & Walter de Wotton, Shebbear

Waltero de Wheddene, Codecombe (Cutcombe adjacent Wheddon Corss)

Just so you understand my thinking I have included any name:
That begins with "W" or "Wh", any vowel next, followed by a "t," "tt," "d" or "dd," another vowel, and an "n"

This excludes Robert de Wibbeton of Kenn, Adam & Robert Withyete (White) of North Molton, Gilbert Whetepayne (Whetpaine) of Teignmouth, Alan de Wabeden (prob. related to William de Wabeden of Abbey de Fecamp in Norman France) of Holsworthy and William Witweye (Whiteway) of Colyton.

But even with these exclusions you can see how many possible progenitors we might have and also how very different names and families could have sorted themselves into the names we see today: Wheaton, Wheadon, Whitton, Wooton. There does not seem to be any consistency with regard to spelling and general location.

The map below is interactive. You may zoom in and out and clicking on a marker will yield more info. I am entering all records as follows:

Thumb tack icons are DNA test proven.

Colors may change with more DNA results or other information, they are somewhat arbitrary.

The following rough outline of Devon's history is also helpful in showing how many different cultures have added to the gene pool from which our various Wheatons descend.

A Very Rough History of Southwest England 
And how this "may" Relate to our Project Members

   35,000  BC Earliest human remains from Kent's Cavern Devon
                      Mesolithic-Neolithic Stone Age
  8-7,000     Hunter-gathers Celtic from mainland to England
     3,800      Burial Tombs emerge in SW England
     3,000      First stage of Stonehenge begins
                      Bronze Age
     2,500      Saracens at Stonehenge erected   
     2,300      "Amesbury Archer" Alpine Celtic buried near Stonehenge 
                      Iron Age
        500      Extensive trading between Devon and Mainland Europe
     50 AD     Devon people known as Dummnoi Language is Celtic 
   43-100     Roman exploration, invasion
 100-410     Roman occupied Britain
  410-500    Celtic rule returns 
  500-700    Celts and Anglo-Saxons coexist in Devon 
  757-829    Saxons extend rule into the Celtic Devon
  700-941    Viking raids on Devon coasts "
990-1003    Danes sack major cities in Devon
1066-1087  Norman Conquest  
1284-1513  Scottish, French Invasions & Wars

Map showing Group B and  L2* matches