legislative issue about permit of stay

Dear All, I am a Marie Curie researcher (early stage researcher, MOTORIST project, grant number FP7-PEOPLE-2013-ITN-608092) at University of Padova since 2014 and I have enrolled as a PhD student in 30th cycle at Aerospace Engineering PhD school (CISAS). My contract will end at the end of September but my final PhD examination will be in 2018. Usually PhD students coming from out of Italy can renew their permit of stay one year more than the period of the PhD in order to attend the final examination and finalize their PhD. In my case, I have been given a permit of stay with title of "scientific researcher" and it seems that I can not switch it to "student" permit of stay and I may lose the last months of my PhD and the final examination. Moreover, my wife who has a "family reunion" permit of stay has also enrolled as a PhD student in 31st Cycle at Department of Industrial Engineering. I was told that my wife may switch her permit of stay to the "STUDENT" one and then she should apply for "family reunion" permit of stay for me which is a very complicated procedure (I know it because I have done it to bring my wife to Italy). I believe this may not be the best way because I have a bank account, contract for housing and I have enrolled as a PhD student in Italy, and usually PhD students do not face such an issue. Moreover, I am not sure in case that I was not married what would happen. Therefore, I would like to ask if you may have any suggestion in order to solve this issue in a reasonable manner? Or you may kindly lead me to a proper contact. Thanks in advance. Best regards, Siamak F. Khosroshahi