Right of an illegitimate child on a propert

I was married 2000. My husband had no birth cert because he was not registered according to his grandmother(his mom is already dead).so we used his baptismal cert instead. Our marriage contract is in Nso. When we were still together with our daughter, he was told to go and work in Japan with his relatives there. But in order for him to go legally, his tita and tito thought of a solution. Given that he has no birth cert at all, they went to civil registry and made a birth cert , the same name but different birthday and parent. His tita in Jpan, was put as his mother as if he was a child out of wedlock.he is now a legal resident in japan.he got there without any problems because in his "new "birth cert his tita ,a resident in japan is his mother.so the person i got married to doesnt exist?but how about the validity of our marriage? I wanted to file it a null and void. Or can i?
Then, i have a new partner now, he is single. We have a son. My follow up question is, does my son have a right to his father's property as his heir. My partner doesn't have any child nor wife before. Because he has land /property on his name , if ever my partner dies, and we are not married, is my child an heir to that property?. Baecause my father's uncle said that my son doesn't have rights over the property, it will go to my partner 's brother and family. My partner's parents are dead.what can we do to ensure our son in the future?pls help!

I can answer this part:

Illegitimate children have inheritance rights too, but when there are more hiers, illegitimate children get HALF share.
(WHEN there are children born inside marriage and/or spouse, then illegitimate child has right to HALF as much as child born inside marriage has.)
I'm not sure, but I suppouse when there are no spouse or child born inside marriage, then an illegitimate child get whole.
So make sure it's proven BEFORE death the child is illegitimate to that person, because later it's much harder to prove.