The Diary of Anne Frank tells the true story of a young girl and her family that were hidden during the Nazi occupation of the Netherlands by a gentile Dutch couple, though they were eventually discovered.
a>that were hidden during the Nazi occupation of the Netherlands by a gentile Dutch couple, though they were eventually discovered
b>that were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands, though they were eventually discovered
c>whom a gentile Dutch couple hid during the Nazi occupation of the Netherlands but were eventually discovered
d>who were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands but were eventually discovered
e>who were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands even though they were eventually discovered
Small question for E's explanation
(E) The pronoun "they" is ambiguous - it could refer to the family or to the couple.
I think here the family or the couple belongs to collective noun, which is singular. "They" is incorrect instead of ambiguous.