Choosing filing status.

hello turbotax, I have the question to choose filing status for this year.  The question is I'm not legally married in USA.  I don't have any legally married certificate to proof.  But I'm used to file as married filing jointly every year with my 2 kids.  This year, can I choose as a single and my wife choose as Head of House Hold to claim with 2 kids?  I want to know about what filing status is the best option. Thanks