Check if it's equal

I have a config were I save players in groups. How can I check If every online player is in the same group?
My code example:
Config:

Code:

group1:
 - Steve
 - Steve1
group2: []

The Code:

PHP:

Task start...
If(/*all players in same group*/) {
//do...
}

 

But I also have other things in the config

 

What about creating an own groups.yml file then?

 

I tried this:

PHP:

$groups = array("G1", "G2");
        foreach($groups as $sgroup) {
$group = $conf->get($this->owner->getServer()->getMotd() . $sgroup);
$names = $conf->get("players");
$tmp = 0;
  foreach($names as $name) {
    if(($key = array_search($name, $group) !== false)) {
      $tmp++;
      $this->plugin->getLogger()->error(array_search($name, $group));
    }
    }
    }


Error:

Code:

array_search() expects parameter 2 to be array, boolean giveN

 

And the result of this is empty

 

Is there another way to do this or how to fix this error?

 

Code:

players: []
G1: []
G2: []