Trouble with YouTube embedding

Site: Novadestin.com, example post

I’ve been trying to adjust the width of multiple videos in my posts, but I’m running into a strange array of issues. If I just use the url, then the video is too large and goes outside of the post width – this is the behavior I want to change. I tried using the embed code and it works on most videos, but leaves some half the size of the width/height I set it too (for seemingly no reason). Using the iframe code works on those, but on others that same code makes the video not even show up. So, getting all the videos in a single post to be the same size sometimes requires iframe and embed codes for the different video links and, even then, sometimes nothing seems to work, leaving a video either too large, too small, or not showing at all. It’s very confusing, and I know it shouldn’t be this complicated.

I changed my theme from Brunelleschi to Twenty Twelve and deactivated all plugins, but this did nothing, so I assume it’s not a theme or plugin complication. I’ve browsed through some Google results on the subject, but couldn’t find anything that really helped. Any ideas would be much appreciated! ^^