I'm new and i have few noob questions

1)

-If i have Dragon Sight:

"If if is Summer,when you declare a challenge type,your opponent must declare defenders before you declare attackers. The opportunity for your opponent to declare defenders after you declare attackers is lost."

and Robert Baratheon (TGM):

"While Robert Baratheon is attacking alone in a challenge, each opponent you are not attacking may declare 1 eligible character as a defender. If you win the challenge instead of the normal claim effects, each opponent must satisfy the claim effect of the challenge."

What happenend if i'll declare a power challenge?

-And, for example,if i'll attack with Robert + another character(whitout Dragon Sight), a player that cannot declare defenders (becouse all your characters are kneeling), and remove my second attacking character after the opportunity to declare defender is gone(so Robert is alone). Can other my opponents declare defenders?

-If my Robert Baratheon (TGM) get deadly who choose the character that was be killed, if a player that i attacking not declare defenders?

2)If i have 2 duplicates on my character and my opponent cancel one with a card, can i trigger the second duplicate?

3) If The Iron Throne (LotR) would be to cancel a response on my dragon, can i cancel the response with Nurtured by the Crone?

Sorry for my bad english and ty to everyone answer me....

1) In the first case, the player you initiated the power challenge against would get to declare defenders, then you declare attackers. Even if you declare Robert as your only attacker at this point, your other opponents can't choose to declare defenders, because the window for declaring defenders is already past.