If the extended paper is submitted to journal, that's fine. But the same paper is unacceptable for publication in the journal. When submitting paper to journal, you need to inform, that the paper has printed at the conference.
No. This is against the codes of COPE. If one does so, his/her paper will not be published. In case it is already published, the article will be retracted. Then the name of the author(s) will enter our blacklist and no manuscript will be ever accepted from the author(s).