Things You'll Need
Instructions
Make sure Selphie is in your party and has learned Full Cure.
Have one character stock Double from Minotaur, and have a secondary spell junctioned on that character to help the percentage rate of not failing.
Keep Squall's HP low so he can use his Limit Break, Renzoukuken.
Have Selphie draw and cast Life on Squall. Do not cure him until he dies. This will allow him to use his Limit Break each time. Using Squall's Limit Break is a key element in defeating the Brothers.
Cast Double for all characters after stocking enough of them. This is because Minotaur has an attack that will take HP from all characters. Double will heal them more effectively.
Cast Aero, Fira, Blizzara and Thundara as attacks.
Cast Float on Sacred and Minotaur so that they can't restore their HP by using Earth Regeneration.
Have Selphie and your other character summon GFs whose element is wind or poison, as these are the Brothers' weaknesses.