My Friend Got Married to a Bigamist

My friend met her husband when she was working in Manila as an accounting clerk. After becoming pregnant, the man, an engineer by profession, informed her that he will be transferred to another city for a new project, but he never came back. My friend searched for him, and there she found out that he was already 5 years married and with 1 daughter. Now, after 12 years of not seeing her husband, she wants to be free of this marriage. The marriage was officiated by a judge and duly registered by the Civil Registrar. A marriage license was also executed and was signed by her grandmother. Her questions are the following:
1. Is her marriage legal or not?
2. Should she file an annulment or not?
3. Will her son be considered as an illegitimate child or not?
Thank you and we will be waiting for your advises in lieu of this dilemma in which my friend is in right now.

if i understand correctly that hers was the first marriage, then it is very much valid and her son is legit.

although she can file a bigamy charge against the husband and the new wife if she knew he was married

Thank you very much for the advise Atty. LLL, I would be glad to relay what you said about the case to my friend.