Thanks for the contributions to solving this sticky little problem. I found that Renee's suggestion that the RM video webnar offers precisely the answer required here, under the heading dealing with duplicate family links. This demonstrates how to delink the husband from the wife first, then you just repeat this for the wife.
So: get the relevent family view on screen, select the husband, and then call up the family view in which the least number of offspring are shown, click on Edit/Unlink from spouse. When unlinked, the father will now show 0 links instead of 2.
Repeat after selecting the wife, and they should now both show 1 link.
I then checked all upward links and all downward links and all were as they should be. Job done!
Thanks again guys!