You should use Gustavus Adolphus for Sweden, and for England you could be different and use Oliver Cromwell. For Prussia, the best would be Frederick the Great, although he was not that much interested in his navy, otherwise, you could use Frederick William, the Great Elector, as Prussia did plant some fort-factories in Africa. For the Netherlands, you could use either Jan De Witt or William the Third of Orange, or just continue to use William the Silent, the existing leaderhead.