I am one my peers in Germany, prepared a journal paper out of his master thesis. We submitted it first to one of the well-known conferences of the field and it got accepted and we let the other coauthors know (including his professor, who is a prominent researcher in his field). They seemed to be very satisfied but due to sudden work load he couldn't attend the conference. Later we decided to extended the paper and I submitted it to journal(not knowing he haven't told the others about submission). The paper accepted in a Scopus indexed journal but this time my peer refuses to make his professor aware. Obviously, they know we have written a paper of the thesis in which their name is appeared. Now I wonder, if I proceed with publication? Is it ethical? What are the consequences if I finalize the publication, for me?

I and one of my peers prepared a journal paper out of his master thesis. We submitted it first to one of the well-known conferences of the field and it got accepted and we let the other coauthors know (including his professor, who is a prominent researcher in his field). They seemed to be very satisfied. 

Later we decided to extend the paper and I submitted it to a journal. I was not aware that he had not told the others about the submission. The paper was accepted by the journal. This time my peer refuses to make his professor aware. 

Now I wonder about proceeding with the publication? Is it ethical? What are the consequences if I finalize the publication, for me?