The confident 6-4, 6-3 victory in the semifinal helped Josef set up a title clash on Saturday with fellow qualifier Tallon Griekspoor of the Netherlands.
Tallon defeated the unseeded Isa Mammetgulyyev of Turkmenistan 6-3, 6-3 in the other semifinal earlier in the day.
Meanwhile in the girls' singles event, Inger van Dijkman defeated fifth seed Lasheen Habiba of Egypt 6-4, 7-5 in their semifinal match.
The eighth-seeded Dutch girl, who won the Grade 4 girls' singles title last Saturday, will square off against Belgian qualifier Estee Widdershoven, who recorded a 6-1, 6-3 win over Russia's Daria Glushich in the other semifinal.
Meanwhile, Latvia's Arturs Lazdins and Justin Roberts of the Bahamas were declared the boys' doubles champions as their opponents in the final, Ireland's Peter Bothwell and Tallon Griekspoor of the Netherlands, pulled out on medical grounds.
Later on Friday, Dutch girl Janine Hemmes and Ingervan defeated the French pair of Apolline Rasat and Julia Soica 6-4, 6-2 to claim the doubles girls' crown.