It's basically a huge plot to hurt the country overall by abusing all kind of...people whose priority isn't the country.
Because Amelia house is managing the country well, if they're destroyed then it'll be easier to put in corrupted nobles and manipulate those.
Though the 'Heroine' aiming for Iris is partly personal hatred of sort.
The Queen is easily to manipulate.
The corrupted nobles will do anything as long as they benefit, missing out any long term consequence of their actions.
Edward is blind with love and already dislike Iris as is.
I forgot what's the church's gain in all this, maybe just hiding their shady dealings since they fear Iris might look into that.