I have seen images on one website under a man's name and the same images on SS under a woman's name. Of course only the very best images they are and all often bought according to SS. How can two people with different genders, once it is a man and the other time a woman, have the copyright to the same images? Is one of them stealing images?

You can choose usernames that aren't your actual name. They could have a business account and both work in a partnership. Lots of reasons. Unless there is another problem, for example using it to skirt excusivity or wildly different styles apart from those images (so one portfolio looks like theft) I would advise not worrying about it.