Suda Masaki will be taking on the role of Ii Naomasa, the adopted son of Ii Naotora, in 『Onna Joushi Naotora』. It will be airing from 8 January 2017 from 8pm to 8:45pm every Sunday. In history, he became a general under Tokugawa Ieyasu and was regarded as one of the four guardians.  The [official website] has updated with relationship maps of the families.
Will update with the Ii family hierarchy.
[edit2] Updated with the Ii family hierarchy.