How come when I click the monster,only my leader attack. Help pls?

did u select all of ur character? i think u only selected 1 character

Theres a button that allows "individual mode" and "select all mode" it's shaped like a triangle.

Theres a button that allows "individual mode" and "select all mode" it's shaped like a triangle.

Or press F9

i find it easier to go into individual mode and just put your characters into groups.
to make a group, select the character(s) you want in the group and push Ctrl+1, Ctrl+2, or Ctrl+3.