The classic red and blue split, in your words
Below the heading strip, option A fills the top half and option B the bottom half, with an OR badge in the middle: the split viewers already know how to play. Every card is a full 1080 by 1920 vertical frame.
Start with red and blue, or switch to orange and purple or green and pink to match your channel. Every question in the set follows the pair you pick, so a series looks like a series.