didn't recognise other roles

I’m afraid the roles are hard coded and the plugin doesn’t detect new ones automatically.

However you might be able to solve your problem. The plugin actually uses capabilities instead of roles. The underlying values are as follows:

Administrator => update_core
Editor => moderate_comments
Author => edit_published_posts
Contributor => edit_posts
Subscriber => read

So if you have a custom role whose highest capability is edit_published_posts then that role will behave just like Author.

As for your second question, yes, several roles can edit a particular post.