How I do this is to add a temporary individual to each unknown person. Then I can merge and then delete the merged temporary person.
Also, I can just add that spouse by number.
After which I can merge the marriages and then the children.
Note, I can only do this when I know for sure that the two individuals are the same person.
How do I merge marriages, when one of the spouse is only a place holder - Unknown spouse?
After merging 2 duplicate persons where the Father was the same person, but the mother was shown as Unknown in the other record, how do I merge the 2 spouses, or get rid of the Unknown spouse?