When such Plots are revealed at the same time, what happens?

How many Intrigue Challenges take place in the turn? One, two or none?

From the main board:

The answer is none.

In this game, the word "cannot" is something of a gold standard or "trump card." If you "cannot" do something, that takes precedence over everything else. With Siege at Riverrun saying that the player cannot declare intrigue challenges at all, it doesn't matter how many opportunities to declare them the player is given. He is always stopped from following through.

Keep in mind that Siege at Riverrun only stops the person who revealed it from declaring intrigue challenges. It has no effect on any other player. So if I reveal it and you reveal Breaking of Oaths, I get 0 intrigue challenges, but you still get 2.

First of all, sorry, for some reason I didn't see your answer in the General Discussion section, which by the way was the wrong section to post in...

It looks like I didn't consider correctly the word "you"... so in fact, the Plot is punishing only the player revealing it; I guess it's the price to pay to get the 2 claim and the good initiative.

Thanks for the answer.