Yes, it does exist. Praying to them is a major Shirk. Lest you be among those who receive punishment. Whoever dies having called upon partners besides Allah shall enter Hellfire. Yes, supplication is worship.
Supplication is worship.
No, they do not hear. But you can not make hear those who are in graves. Allah Has assigned angels to inform me of my nation salutation. No we do not seek help from, we rather seek help from Allah. No, it is not permitted.