This is done at the start of disc 3 when you go back to
They are found in the weapon shop and only available when controlling Zidane.
This minigame starts with one of the brothers saying their name then shuffling around with their other 2 brothers. You need to watch carefully then select the correct brother. You need to guess correctly 9 times in a row with each round getting faster. You also cannot select 'Don't pay' to leave or save as this will reset the game back to round 1.
The best method I found of winning is to use my iPhones slow-mo video mode, record the screen then watch it back on your phone, then select the right brother.
Other methods which people have suggested are to use an app such as VLC to record the screen then watch it back in slow-mo.
The only issue with these methods is in the last 2 or 3 rounds the framerate can make it quite difficult to see where the correct brother is jumping too, but just keep looping that video and pay attention.
Hope this helps!