I have three questions, 1. My oppenant attacks and i block with my Avacyn, Angel of Hope he then gives the attacker Proection from White, is the block still legal or does it get through?
1) Once blocked, a creature stays blocked. Making the block illegal after the fact won't do anything.
2) He loses 4 life, in two steps of 2. First he takes 2 combat damage, then the Guildmage's ability kicks in. When its delayed trigger resolves, he loses 2 more.
3) Yes, you have to pay for each extort trigger seperately in order to drain your opponent.
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"Simple questions" usually need rather complex answers, while complex questions often come down to no more than a simple "yes" or "no".
1. the creature deals damage to avacyn, angel of hope and the damage from avacyn is prevented. Since it was after the declare blockers step then the creature remains blocked. If he had given his creature protection form white before the declare blockers step then you would have been unable to block.
2. There is a time during the declare blockers step when you can activate vizkopa guildmage knowing your vampire nighthawk is unblocked but before the damage is dealt and before you have gained the life. Therefore he will lose two life from the damage by vampire nighthawk and you will gain two life at which point he will lose another two life from the vizkopa guildmage ability.