The elder sister is called Wanjun, the younger brother is called Jianjun or Baojun, both are fine.
They both have a homophonic word "jun", which means they are siblings.
It may also be called establishing an army, benefiting an army, establishing a king, benefiting a king, guarding an army, defending the king, then king, and then army.
You can also name it independently, whatever you like, it doesn’t have to be related to your sister’s name.