Hi need advise asap..

My mother and father married under catholic rites and had 3 children. then he converted to muslim to marry another muslim woman 5 months before there twins were born. this happened in 2006 without the knowledge of my mother and us. Can this be considered bigamous marriage? what case can my mother file? my mother wants to pursue a legal separation case and a separate bigamy case? until now, my father does not know that we know anything about his second family. please advise asap. can we ask for philippine jurisprudence similar to our case? appreciate your legal advice.. thank you in advance..