Janet, I have thought for a long time that the lady who is partially obscured by the pillar is Princess Helen, Princess Christian.
I think (but am not 100% sure) that the lady seen at the far right hand edge of the detail below is Princess Louise, Duchess of Argyle -- but I admit I could be very wrong.
I have also thought that the lady in front of Queen Mary is the Duchess of Albany, possibly wearing the Indian tiara which had been given to Queen Victoria.
To me the real mystery is -- who is the lady sitting almost directly behind Queen Alexandra?