I believe the following is a duplicate. However, I'm unable to combine them. ;
Marianne Hiscock: GZV9-MSL and Mary Ann Hiscox: 2SDS - NWS
FamilySearch does not have a method to ask and receive answers to questions regarding the above.
Since these two individuals have the same name, same birth information, same death years and same parents, it does look appropriate to merge them.
The possible duplicates routine seems to never present siblings. This is good because there are areas of the world where if a child died, the next sibling of the **** would be given the same name and through the years too many people have incorrectly merged such siblings. It is also unnecessary because any duplicate of a child will be sitting right there in front of us as these two are.
To merge them, you need to use the Merge By ID function found in the right hand column under Tools. Start on one of their pages, copy the ID of the other one, click on Merge By ID, paste in the ID then proceed.
Family Search does indeed have several methods to ask for and receive answers to question such as these. Currently, the main one is to post your question here, just as you have done. You can still call. Or you can visit your local Family History Library if there is one near you.