Envoie mail tous les membres

Bonjour, j ai recupere un site et je voudrais ameliorer ce script pour q uil envoie un mail a tous les membres une fois que la guerre est cree
createwar-form.php?

<form action="components/create-clanwar.php" method="post" enctype="multipart/form-data" id="UploadForm">

        <div class="col-md-6 col-md-offset-3 panel" style="padding-top:15px; border-radius:25px; border:solid #999 2px;">
            <div class="col-md-10 col-md-offset-1">
                              <h4 class="text-center profile-text profile-name">Nom du clan</h4>
                  <div class="form-group float-label-control">  
              <input name="war_enemy" id="enemy_clan_name" class="form-control" type="text" placeholder="Nom du clan ennemi" required="required"></input>
                    <input name="war_warid" type="hidden"></input>
                  </div>  
                  <hr>
                  <h4 class="text-center profile-text profile-name">nombre</h4>
                   <div class="form-group float-label-control"> 
                        <select name="war_size" class="form-control">
                        <option value="50" selected>50 vs 50</option>
                        <option value="45">45 vs 45</option>
                        <option value="40">40 vs 40</option>
                        <option value="35">35 vs 35</option>
                        <option value="30">30 vs 30</option>
                        <option value="25">25 vs 25</option>
                        <option value="20">20 vs 20</option>
                        <option value="15">15 vs 15</option>
                        <option value="10">10 vs 10</option>
                        </select>
                    </div>  
                    <hr />
                  <h4 class="text-center profile-text profile-name">Démarrage de la guerre dans</h4>
                   <div class="form-inline text-center"> 
 <input  class="form-control" name="hours" step="1" min="0" max="23" value="23" style="width:60px" type="number">
  heures et 
 <input  class="form-control" name="minutes" step="1" min="0" max="59" value="59" style="width:60px" type="number">
  minutes.
                    </div>  
                    <hr />   
                  <h4 class="text-center profile-text profile-name">Temps restant pour réserver</h4>
                   <div class="form-inline text-center"> 
<input  class="form-control" name="call_timer" step="1" min="0" max="24" value="5" style="width:60px" type="number"> Heures
                    </div>  
                    <hr />                                      
                     <div class="form-group float-label-control"> 
                     <div class="submit">
                     <center>
        <button class="btn btn-primary ladda-button" data-style="zoom-in" type="submit"  id="SubmitButton" value="Upload" />Lancer la guerre</button>
        </center>
    </div>
                     </div>  
   </div>
        </div> 

 
</form>

a l execution de ce script je voudrais q u il envoie un mail a tous le monde avec ce script

mail.php

?php
    ini_set("display_errors",1);
    if(isset($_POST)){
	$username = htmlspecialchars($_REQUEST['username']);
	require '../_database/database.php';
	$sql3="SELECT * FROM user WHERE user_username='$username'";
        $result = mysqli_query($database,$sql3);
        $user = mysqli_fetch_array($result);
			
 if(count($user)>=1){
	header("location:../controllers/form/createwar-form.php?"); 
	
        $message = "La guerre est declarée.";
	$user_email = $user['user_email'];	
	$name = $user['user_firstname'];
	$user_username = $user['user_username'];
				
	$to = $user_email;
	$email_body = 'Hi '.$user['user_username'].', <br/> <br/>Your UserName is '.$user['user_username'].' <br><br>La guerre est déclaré.N oublie pas de reserver ta cible et penses au remplissage des cdc. ';
	$headers = 'Mime-Version: 1.0'."\r\n";
$headers .= 'Content-type: text/html; charset=utf-8'."\r\n";
$headers .= "\r\n";
 
	mail($to,$email_subject,$email_body,$headers);	
	header("location:../controllers/form/createwar-form.php??send");
	die();
}else{
	header("location:../controllers/form/createwar-form.php?"); 
}
   } 

D avance merci