[Plugin: Posts 2 Posts] posts 2 users

Not sure what you mean by ‘simultaneously’.

It also depends if the relationship is:

post_A - post_B - user

or

post_A - post_B
post_A - user

I have 2 different post types, say posts A and posts B.

They are connected.

But posts B are also connected to users.

Now, for each post A I want to list all connected posts B, and users connected to each of those B posts.

Well, something like this should work:

$connected_B = new WP_Query( array(
  'connection_type' => 'A-TO-B',
  'connected_items' => $post_A
) );

p2p_type( 'B-TO-USER' )->each_connected( $connected_B );

The trouble is that each_connected() doesn’t work for posts-to-users connections yet.

I’m not sure I understand… so this won’t work at the moment? If it will, could you let me know how the rest of the code should look like, how to finish the loop, I’m a bit lost here…

It now works in the development version (1.1.5-alpha).

You’ll find a complete usage example for each_connected() in the wiki:

https://github.com/scribu/wp-posts-to-posts/wiki/Looping-The-Loop