Vicky - your friend, Dani is not entirely wrong - just perhaps a different interpretation. Good you raised the topic though; very interesting.
Sailvic: because the odds are different from winning a lottery prize does not mean multiple births by different mans is spurious. It isn't something that families would broadcast. The medical accounts I read were from several historical records made in Scandinavia during the 1950s and from West African research in the 1980s. It isn't rocket science - sperm from different men impregnanting two different eggs with the same woman is, when one thinks about it, probably more common than thought. One of the Scadinavian incidents came to light as one baby was black and one was white. The white husband divorced the "cheating" wife on those grounds. Probably had she conceived by two white guys then no one would have been any the wiser.
The old aphorism that it is a wise young who knows its man is maybe less enigmatic than previously now that we have sophisticated DNA profiling - however certain cultures such as the ancient Celts recorded descent in the female line so maybe they were wiser than we imagined.