problema sa property

my mother died early so after few years my father got married again with my stepmother but after a decade my stepmother left to USA and got married there again after 14 years she came back and ask about the property, the property was named to my father and stepmother but it was before with my mother when they acquired the property. at the first marriage my father has 2 siblings me and my eldest brother at the second marriage my father has 1 son and an illegitimate child my question is what is the right of my father to give the 3/4 of the property to his first 2 sons and 1/4 to his second marriage son?And what is the right of my stepmother?

1. Mother die:
I haven't read the law, but for a common case as when your MOTHER died, I got such information:
Mother had half. Your and your brother split HALF of that  = 12,5/100 each of the WHOLE.
Father get that too.   The last 12,5/100 can the owner decide about, but the answer I got don't tell what happen when there are no will.  
2, Father die:
ASUMING your father got the last part from your mother. Then he had 75/100
IF no special document was signed separating this, when your father married again - which I suppouse NOT was done - then the stepmother got half of that by the marriage.
Half of your father's remaining 37,5/100 is split equal between the kids UNDEPENDING of illigemate or not. = 9,375/100 to each kid.
Stepmother get same. The last 28,125/100 father could decide himself who get it IF he wrote a will. Otherwice that part is unclear.

Summary: AT LEAST 12,5 + 4,6875= 17,1875/100 (=a bit over 1/6) EACH to you and your older brother. Plus PERHAPS some of the two unclear parts.