Where does it state that the twins were 'not' identical? The fact that several people were unable to tell them apart would indicate differently?
I haven't seen anything referring to the twins as fraternal or identical I was just going on images in the public domain and to my eyes they don't look identical. They are mostly dressed differently too. I don't recall CC's book referring to them as identical or that people couldn't tell them apart.
Who were the several people? I'm only aware AE said she had difficulty in differentiating, who were the others? It seems to me AE only saw them on the odd occasion and hadn't seen them for some considerable time. They obviously look similar and being the same age/build would make it difficult perhaps for someone like AE who only saw them infrequently and hadn't been in their company for some time. JM put them to bed at the party on the Sat before. A member of the Howie family offered to identify all victims so I'm assuming he/she felt able to do so.