Hello,
As per the law the son of the first wife will have equal share in the property.
Also you may please note that you being the second wife will not be entitled legally to any share. However your son ill be eligible. This has been held by the Apex Court. Reference of the case can be seen at : http://www.thehindu.com/todays-paper/tp-national/Second-wifersquos-children-not-herself-entitled-to-property-apex-court/article15155341.ece
Regards
Correct me if I am factually wrong.
Regards