No. "Yourself" is unnecessary and the verb "to be" is improperly conjugated. The sentences should be: You are responsible for that. You can use "yourself" for special emphasis if you want to, but it's uncommon. With it added it would be: You, yourself, are responsible for that.

No this doesn't sound natural to me. The 'yourself' bit isn't necessary but as has been said before, you can add it for emphasis, however, I would add it at the end: You are responsible for that yourself