Is it permissible for the son of the paternal uncle (from my father's second wife) to marry my full sister (from my father), knowing that there was suckling between the children from the first marriages but no suckling between the second marriages, and that both spouses have children?

What matters for the prohibition of marriage due to suckling is the presence or absence of suckling. There is no suckling between your paternal cousin from the second wife and your paternal half-sister (the daughter of the second wife). So, they are paternal cousins, not siblings, and it is permissible for him to marry her.