Can my brother get child custody of his biological child

Hi! My self ..need ur valuable advice in child custody...my elder brother having 4yr boy from a lady , documentaly they r not married ,brother was devorcee and lady was widow ...till now no proof on paper as marriage.....we r Buddhist by religion she too...Lady had negative history to harass her husband who had committed suicide and she is availing his pension posthumously......she had built relation with my brother as he was devorcee and had distance relatives....to get financial, social esteem as our family is socially well off .......now becoz of her troubling nature sour relationship bet them.....as being illiterate lady , vry backward ,remote trouble village native place ,logically she can't give child a accessible amenities as we will provide him in future.....after failing to reconcile her .....we need boy custody as father ....kindly suggest legal Angle ,possibilities to win custody