Getting right object of group

I want to add tail to rockets in my game because some of them are dark and besides it look cool. So I decided to use particle system.

The “Bullet” (hasn’t decided if it’ll be bullet or actual rocket) and tail are in one object group. Positioning “tail” direction of particles against bullet/rocket movement shouldn’t be hard.
Unfortunately though I don’t know how to pick right objects so bullet and tail would be in same group instance (so I don’t get funky result like tail positioning against rocket that is flying in opposite direction). How to do that?

Groups are not meant to be used for these purpose and won’t be of a great help.

Instead, take a look to the “Linked objects” extension. When creating a rocket, and its tail, use the extension to link (virtually) the objects together.
Then, if you’re for example iterating over all rockets ( using a for each event ), you can use the appropriate action to get the associated tail object.