1) The Force fight would be extremely difficult. As of Dark Empire, Palpatine is superior to Kun - but seems to only have gained his Force Storm abilities and regained his former lightsaber prowess. Other than that, his powers seem to be the same. Adding Maul with the Emperor, I see Kun losing.
2) I see Kun winning. Palpatine probably hasn't practiced with a lightsaber, instead devoting his energies to expanding his strength in the Force. And Kun > Maul.
3) Difficult. Kun will overwhelm Maul, but Sidious will be harder - due to his Force powers. If Kun can force Palpatine into a lightsaber battle, he'll win.