Event invitation

Hi all,
I am running Drupal 7 on my website. I have two main different user roles (running profile2 also) : interviewer and interviewed.
I would like to let the interviewers to create an event “interview” (I used a specific node type so far) and register to it (which I made it work with different modules as flag, signup, entity registration or node registration).
However, there is one thing I didn’t found how to do, is to be able for the interviewer to “invite” one of the user interviewed to that interview. (by a user selection text field). The maximum of participant to the interviews is always 2. The target should be to received this invite as a yes/no question as a private message for example.

Is there an easy way to do that with Drupal 7?

Thanks a lot for your help,

Drupal version: 

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