Set widths on both iframes/div and float left
Basic CSS…
<html>
<body>
<iframe src="https://www.twitch.tv/CHANNEL/embed" style="width: 200px; height: 200px; float: left;" />
<iframe src="https://www.twitch.tv/CHANNEL/chat" style="width: 200px; height: 200px; float: left;" />
</body>
</html>
Above is quick and dirty and probable doesn’t work, but serves as an example 