Based on my research, lack of authority of solemnizing officer is ground for declaration of nullity "unless such marriages were contracted with either of both parties believing in good faith that the solemnizing officer had the legal authority to do so." That made us lose hope on filing for case on that basis.
However, is forgery a ground? Can it be considered if the signature of one of the witnesses in the Certificate of Marriage was actually forged? It was a "shotgun" marriage since the wife was pregnant at that time and her family "required marriage".