Complex sentence: Upon Muneyoshi's death in 1606, the school split into two, his elder son Yagyū Toshiyoshi taking command of the Owari branch, while Munenori became the head of the Edo branch.
Split into simpler sentences: Upon Muneyoshi's death in 1606, the school split into two. His elder son Yagyū Toshiyoshi took command of the Owari branch, while Munenori became the head of the Edo branch.