if you select a profile and click the arrow at the top to change between them you can see the silhouette and will have a hint. Otherwise I’m not sure who without an image. 2 probably could be from yui’s story. One being Cassandra which you will need to have completed Shizuka’s trial and make sure it isn’t December in game. Then go to the outside part of the dojo.
As for the other 2 could be Luna who is the witch that you can find at night on the map. Others I’d check other locations you haven’t explored yet or main stories not caught up yet maybe