I've not used the dreaded, bloated resource-hungry RealPlayer for over a decade, so I can't answer that one. Sorry!
Basically you just need DVD burning software which accepts the file formats that you get when saving Youtube videos. My last post here might be relevant. It refers to excellent software, which I've used myself, but I've not actually burned video-DVDs with it. (I've only used it for date DVDS). So I can't guarantee that it will work:
http://www.theanswerbank.co.uk/Technology/Question1403609.html