Tatsumi wears a wigIn the anime and the manga, Tatsumi is bald and doesn't hide it. This story's version of him has black hair. It's probably a wig.
The false Athena is SeikaSeiya's big sister went to Greece after him, lost her memory and wandered around until the Big Bad found her and decided to pass her as Athena to keep the saints from realizing Saori Kido is the real deal. It'll be revealed in the sequel if one is made.
The 3 unnamed enemies from the beginning are actually Silver or Bronze SaintsThey are often referred as ordinary soldiers from the Sanctuary, but in the manga (and in the original anime series) the Sanctuary never sent ordinary soldiers to eliminate their enemies.That would also explain why they were considered to be relevant enough to have a cameo in the last scene