Can I make my YouTube Videos smaller?

Yes the videos are rather large indeed!

I suggest you try and force the size change through css. Try this (in wordpress go to apperance>editor>vantage: Stylesheet(style.css)

Add this:

.fluid-width-video-wrapper iframe {
     left: 130px !important;
     width: 75% !important;
     height: 75% !important;
}

Let me know if this works, and adjust the width, height for size and left to keep it central.

The way I do it is to use the Page Builder plugin (another SiteOrigin product) since I am already using it to build my web pages anyway. For your case, all you would have to do is create 3 columns, place the embedded video in the center column and leave the other columns empty (or add text if you like). Then, using the mouse, you can adjust the width of the columns and change the size of the video to your liking.

In my case I have 2 columns and a sidebar. Here is my web page to show you what I mean. The page was built using 12 rows, and both single and double columns, arranged in a manner to handle the layout of the various text and video items.

https://www.flaminghellmet.com/launch/videos/