Photos insists on renaming a face because sisters look so much alike. I rename, but photos reverts back. The "make key photo" does not highlight. Suggestions. Thank you

When Photos has merged two people into one People album, because they are frequently appearing together in one photo or are very look-alike, then I would not use the "confirm additional faces" dialog. It may just add the same incorrect names back.

What I have done in such a case is renaming all faces individually, sand at first with two new custom names for the two people, that are not in the Contacts.

• First, create a standard album for all photos where the name needs correcting. You can select all photos in the mixed People album with ⌘A, then create a new album for the selected photos.
• Now enable the option View Show Face Names. This way you will see faces circles with a name tag, when you view the photos in the album enlarged.
• Now open the album, enlarge the first photo, type the new, temporary nickname into the name field below the face of person. Type a new name below a face of the second sister.
• Now Switch back to the People album. You should be seeing two new albums there, one for each sister.
• Now open again the album with the images of the two sisters, where the names need to be corrected. Step through all photos and correct the wrong names, until all faces with a wrong name have been corrected.
• When done, quit Photos, and make a new backup of your Photos Library to save your work.

I would wait a while with reverting back to the correct names from the Contacts card, or Photos might merge the two sisters again.

See also: How to Correct Merged People Albums - Apple Community

léonie's solution is fascinating and brilliant!

I would add that you should include a keyword for each sister who's in each photo, and maybe who is left and who is right in the description/caption. Face identifiers get lost in OS upgrades and exports, while keywords persist. You may be faced with doing this all over, again, and keywords would be a big help.

You're welcome. Good Luck 😊

And I second Richard's suggestion to add keywords. It will preserve your work and make it possible to check the assigned faces with smart albums, if you suspect, that the faces got mixed up again.