If you’re logged into WordPress as an administrator, you can easily change the post author of a post to someone else.
So what you’ll want to do is set up different user accounts for your different authors and then set yourself up as an administrator. Then when you go to publish a post using your administrator account you can select which author you want it to be published under.
This video is old, but it more or less outlines the process of what you’re looking to do: http://wpu.me/change-post-author/