Does a grandmother's suckling of her grandchild count as valid suckling if she is not in a period of suckling one of her own children, and in this case, does the grandchild become a paternal uncle to his maternal aunt's daughter (his paternal aunt's daughter) through suckling?

If your grandmother breastfed your paternal aunt's son five full feedings or more, and he was under two years old, then he becomes her son through fosterage. Based on this, he is considered your paternal uncle through fosterage, and it is unlawful for you to marry him. This is because a woman's milk spreads حرمة (prohibition of marriage), regardless of whether she is married or not, as long as the conditions are met, which are five full feedings within the first two years of the child's life.