Normally, when post video’s news in website or upload video on YouTube suddenly Facebook or Twitter can take a whole news which you posted, so when you share URL or video YouTube to Facebook or Twitter, it will appear thumbnail in a small form or other forms which difference from what you want.
The solution you can Clear Cache URL in Facebook or Twitter in order to Facebook or Twitter take new form of what you want.
Facebook clear cache
Twitter Clear cache
These are the best solutions to Clear URL on Facebook and Twitter.