Wikipedia is inconsistent (SURPRISE!)
http://nl.wikipedia.org/wiki/Rudolf_II_van_Coevorden states that Rudolf and Sophia had three children BUT then further down the page it mentions "...Eufemia, de dochter van Rudolf...".
Nothing to suggest a mistress so presumably Euphemia van Coevorden is the daughter of Sophia, as shown on Geni.
I think there is a hint of the underlying cause of this inconsistency if you compare the wiki.nl page to the wiki.it page.
The Italian version uses the wording "dalla quale ebbe tre figli maschi (Bertolt, Heino Henrikus e Cyse)" which Google translates as "...he had three sons..." as opposed to the Dutch version's three children.
This interpretation gives us the opening that Rudolf and Sophia could have had ten or even twenty daughters as well as their three sons. However the problem then becomes explaining the fourth son that Geni shows, Volker van Echten, Heer van Echten.
I have checked Dutch, German, Italian and English Wikipedia's but none mention Volkert van Echten.
Googling the name Volkert van Echten bigs up some interesting sites.
Reading this site: http://www.regenboognoordscheschut.nl/digitale%20omgeving%20Noordsc...
Combined with wikipedia:
http://nl.wikipedia.org/wiki/Coevorden
makes me wonder if Leffart van Bierum and Ludolf van Coevorden are actually the same person?
