While long drawn to the Lutheran faith and always seeking balance between Protestant and Catholic factions, Joachim II did not officially profess the Lutheran Creed until 1555. This may have been the result of promises he had made to his father and to his second wife's family. Joachim I had had his sons sign an inheritance contract to remain Catholic; had Joachim II not signed this pact, he would likely have been passed over in the line of inheritance.
Joachim II's first marriage was to Magdalene of Saxony. (Apparently, she stopped being his wife...died?) In 1535 he married Hedwig of Poland, daughter of Sigismund I (the Elder), the Jagiello Grand Duke of Lithuania and King of Poland. The Jagiello family were Catholics and Joachim II promised her father not to make her change her religion.
In 1545 Joachim II held a gala double wedding celebration for his two children, Prince Johann Georg and the Margravess Barbara. They were married to Sophie and Georg, both children of the Piast Duke of Silesia, Friedrich II.