Separate Registration and login for different roles in wordpress

I've set up 2 new roles for my site using the "Members" plugin - "sellers" and "buyers".

Each role should have its own registration page and login. A visitor can register as both a buyer and a seller but he can only be logged in as one of them. So, if a visitor has logged in as a seller and then goes to the buyer page he'll be able to login as a buyer and when he does so he will automatically be logged out as a seller.

I've searched for hours for a plugin that will give me the option to do this but couldn't find one. Sounds like a pretty common configuration in websites with different role registrations.

Does a plugin such as this even exist? And if not how can this be done?

via Chebli Mohamed