Well, if they provide an embed code then that’s fantastic. Why do you need the carousel of thumbnails? What specifically are you trying to accomplish?
I know these may sound like daft questions but it seems like you are really asking a website (yours) to do much more than it’s really capable of with iFrame cropping and/or any cropping of a page. My guess is that’s a fruitless and maddening endeavor.
… but there are ways to display a grid of other videos through various means. Perhaps you could give a screenshot of what you are looking to accomplish. My guess is another design alternative will work much better for you, but we’d need to actually see what you are trying to accomplish. It would also be useful to know about how many videos you have, how many you’d like to show in a carousel or grid, and any other relevant design details.