How to add multiple YouTube subscriber counts together - php

Question

I own a YouTube Network. For those of you who don't know what that is it's a alternative to YouTube's Ad Sense service effectively. Anyway, we have a control panel that we didn't make that tells us the total combined subscribers of all of the channels on the network. I thought that would look quite nice on our website as it may encourage people to choose my network over others. This is what the control panel looks like - https://i.imgur.com/ZfuH4BJ.png I asked a question on there comuntiy and there answer was along the lines of "It's pointless us making our API as everything we do is from YouTube's Data API. So I googled YouTube's Data API and yeah I managed to get it to work but only with 1 channel. The only way I can think of making a count on my website like the one on the control panel is by manually adding the channels into like a sum of adding the queried channel subscribers together. Also when new channels join the network it could be up to 100's per day so I wondered if there is a way to query the control panel to see when new people join the network and then send it back to my web server and add it into the code automaticly?? Below id the code of my page on my website that I display the data `
<!-- Gather YouTube Subscriber Count (PHP) -->
<?
// Calling api.
$subscribers = file_get_contents('https://www.googleapis.com/youtube/v3/channels? part=statistics&id=channel_key&key=api_key);
// Decoding json response
$response = json_decode($subscribers, true );
?>
<!-- Navigation -->
<nav class="navbar navbar-default navbar-fixed-top">
<div class="container">
<!-- Brand and toggle get grouped for better mobile display -->
<div class="navbar-header page-scroll">
<button type="button" class="navbar-toggle" data- toggle="collapse" data-target="#bs-example-navbar-collapse-1">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand page-scroll" href="#page-top">RiteSide Network</a>
</div>
<!-- Collect the nav links, forms, and other content for toggling -->
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav navbar-right">
<li class="hidden">
</li>
<li>
<a class="page-scroll" href="../index.html"><i class="fa fa-arrow-left"></i> Return</a>
</li>
</ul>
</div>
<!-- /.navbar-collapse -->
</div>
<!-- /.container-fluid -->
</nav>
<header>
<div class="container">
<div class="intro-text">
<div class="jumbotron" align="center" style="color:black;">
<h1>Partners</h1>
<br />
<p>Please Come back soon. This page is almost finished!</p><br /><br />
<h1>Subscribers: <? // echoing subscribers count.
echo $count = intval($response['items'][0]['statistics']['subscriberCount']);?></h1>
</div>
</div>
</div>
</header>
<p> </p>
</body>`
Any Help is greatly appreciated! If you need any more details explaining, just say.
Thanks! Charlie :)