split wordpress

Hello,

I have a wordpress share site closed to unregistered users. There are about 40 people registered as subscriber and 5 writer. From now on I want to include more subscribers, but topic will be different and I want to seperate them (same wp db but categories, etc will be seperated)

A writer will publish post to group which he choose or both of them

Is there a plug-in ?

I can build another WP site, but don’t want writers to enter login infos over and over.