Upfront Scribe Theme YouTube Embed Issue

When using Upfront editor's drag & drop YouTube element, only the option for a YouTube URL is available. Without the ability to insert ?rel=0 (as in using iframe embed code) I cannot prevent YouTube from showing related videos at the end of my video.

I tried using the drag & drop "Embed 3rd Party Code" element and adding the YouTube embed code with ?rel=0 and that does insert the video and prevent related videos from playing.

That said, then the video is not responsive.

How can I both prevent YouTube from playing related videos AND make the video responsive?