What is the relationship between me and whoever was nursed by my paternal grandfather's first wife (my paternal grandmother), and what is the relationship between me and my paternal uncles' children from my paternal grandfather's first wife, given that I was definitively nursed by my paternal grandfather's second wife?

If you nursed from your grandfather's wife, then you are her son and a brother to everyone she bore or nursed. You would also be a son to your grandfather through nursing, and consequently, you would become a brother to all your paternal uncles and aunts. It is not permissible for you to marry their daughters because you have become their paternal uncle through nursing (due to "milk from the male"). As for a man who nursed from your grandfather's wife five full, satisfying nursings, he becomes your brother and the brother of your paternal uncles through nursing.