Hi - I'm still not clear on why the family thinks the Splans originate in Denmark? Who told that story to whom - or did someone write it down? But yes, anybody in a place raided by the Vikings centuries ago could conceivably have Danish blood. Few Danes can trace their heritage back that far (as far as I know) as records from so long ago were mostly only kept for nobility. A typical ending point in Danish research is the early 1600s. You'll have to trace your Splans back to Scotland and back from there to reach any Danish link, so where you are at now in your research (not having identified Samuel) is too early. First ask your Splan genealogy questions; work back one step at a time.
Splan is not a Danish name. It does not remind me of a longer name that could be Danish. One idea would be for you to check Danish place names - as this could be a Danish place name (or a variation of a Danish place name). A much-used database for that is called Krabsens:
Otherwise, check Danish male first names. A Danish man would have a "surname" based on his father's name + sen (such as "Ole's son"). So a Danish form would be Splansen. Could that be Svensen, or Paulsen, or...
Checking into names is something you can do now. However, if you consider the connection could be as far back as 800 AD, I do not know why your family would still have family knowledge of that. Thus still yet another consideration might be that there is an "extra matrimonial" incident (an out of wedlock connection) that is partly known and partly not. Perhaps you can brainstorm still more reasons for the story. You may have the key to the mystery yourself, in uncovering the origin of that very odd and unlikely story.
About Elizabeth Weston - I also was confused by the two Elizabeth Westons, but apparently the maker of that family tree has identified a connection. I'm glad that finding the tree was helpful!