Ignoring the clowns and the taunts, we have that none is capable of harming the seraphim. Unless maybe Luffy and Zoro use the advcoc.
And please, Sanji has used an attack with his most powerful form, the IF, Zoro and Luffy have not yet used their respective PU.
Lastly, if even with everything, they are impossible to damage, the King vs Zoro fight would have been a huge mistake on Oda's part, making King switch to speed mode