Fake NSO Birth Certificate used in their marriage

I'm a mom of 2 kids but not married to their daddy.
Hirs the scenario.
His not legally adopted by his foster parent's because of some issues.
Then he decided to get an NSO Birth Certficate using the SURNAME of his foster parents w/o their consent with fake signature and thumb mark then he got married to other woman that he got pregnant. When his parents check in the CITY HALL they had a marriage certificate already. He was actually going to be adopted by his foster parent's but bcoz of this marriage thing that he did his parents got mad and decided to get him a LATE REGISTERED NSO Birth Certicate using the SURNAME of his biological mom. My 2 kids and der step-sister was using the SURNAME of the FAKE Birth Cert of their Daddy. My Ex wanted to void the marriage because of some issues between them and the allowance of my kids was affected. Pls help.

So the question's are:
1. Was der marriage is valid or not?
2. If not valid or void what step they need to do to void their marriage certificate?
3. If we don't file a case to their marriage will it be valid in time? for how long?
4. If their marriage cert will be void the next prob will be the SURNAME that he used to his 3 kids right? So wat will be the steps of changing the SURNAME of the kids?

Thank you..

Hi, Me and my wife got married last 2003, i know she was just 17 y/o during that time. but when i look at her birth certificate and our marriage cert, its not same. marriage cert says she was 18 and birth says she in 17th during that time. she told me, they fake her age so we can get married. wow, didnt know about this. is our marriage valid? do wrong information provided during marriage will void the marriage?