The Black Panther will involve the mountain lions that they met on the way to the capital
ES Hines said in a newspaper article that her favorite animals were lepords and jaguars, and that she'll be writing about them in "The Black Panther." The mountain lions are the only other big cats mentioned in the story, so therefore they must be important too. There wasn't really a reason for them to be there other than to show up later
Adrian and his brother are the same person
And his double identity is all part of a huge plot to take over the world. Darius knew that the council wanted peace, and he knew that he had to search for Bria to make sure that she never came back to take power again. He had a plan to gain power when they were trying to make peace, but he also needed to stop Bria from ever returning. So, he crafted a double identity to gain her trust all the while pinning his "strangely identical brother" as the villian. Now that Bria is in love with him, he will have a much easier time controlling her in his quest to take over the council.