If you don't have Cat Nip or a high Level, it might be very hard. The first time I faced them, I killed them (Barely
).
If you have the Alchemist Dressphere, use it to make mixes.
Click here for a Mix List.
If you can't keep up with them, try using Rikku's Special Dressphere: Machina Maw. The Special Attack "Vajra" causes uber damage to any enemy. Be aware that the Magus Sisters have high dogding abilities, so sometimes they may not get damaged.
If you do have Cat Nip, USE IT! Using a Gunner's Trigger Happy or any other Dressphere that has an ability which can attack the whole enemy party, they'll be killed in seconds! =D
Happy killing!
