Its a bit unclear as to what you are trying to do so I hope my answer helps.
If the $poster, $topic, and $message variables are set in forumsnews.php and servernews.php then you would need to include those files before you call the variables. And you would only need to include them once.
Now since the $poster, $topic, and $message variables in the servernews.php would override the $poster, $topic, and $message variables in forumsnews.php you have to place your includes accordingly.
Generally speaking it is bad technique to reuse variable names, as you have. There are cases were you can but for your situation it could cause problems.