Family connections to whom be can marry

Assalamualikum i'm confused in my case my grandfather has 2 wife's. So ,first wife had 1 son(he has childrens in that one son(**his daughter**)) and she(1st wife of grandfather) died and he maried again for her children in that one son of son is i am. so basically her dad and me is brothers and i like his daughter so we can marry....