Mistake in correction.

Question

In the exercise entitled "A Book Lover," there is a phrase "...rien qu'en observant ses grands frères et sœurs." When I entered that spelling, the s's at the ends of "frère-" and "sœur-" were marked as incorrect even though they were present in the correct example.

In passing, if Damien indeed only had one brother and one sister, would we have to say 'son frère et sa sœur'?

Thanks a lot.

Céline Pickard · Accepted Answer

Bonjour Andreas,
I wrote the exact same answer as you and Kwizbot gave me a "Well done!" feedback with two alternatives answers:
"the best answer is rien qu'en observant ses grands frère et sœur" (with the -s crossed in red)
and
"you could als say rien qu'en observant ses grands frères et sœurs"
However, I can understand why it would give you the impression that your answer was marked as incorrect. I have flagged this with the team for them to take a look at.
Here, you could have:
"ses grands frères et sœurs" -> referring to several siblings
"ses grands frère et sœur" -> referring to exactly one brother and one sister
 
I hope this si helpful.
Bonne journée !