The absolutely necessary two members are Carina and Aka. Aka debuffs and then, crucially, uses poison during phase 2. After that simply turtle.
Carina is needed to heal and buff defense of course. Make sure everyone has at least a single layer of defense buff, preferably double. In phase 3 Fate has an attack called Null Zone or something that deals insane damage.
That leaves the final member. Qum is ok but without any offensive spell the fight will be long. My recommendation would be Vhala or Hilstara.
Vhala: helps with the debuff, tanky so she won't go down easy, and decent damage
Hilstara: super tanky, can help Carina with buffing, and good damage
Between the two I'd say Hilstara's better, since during phase 3 Fate loves spamming insane AoE attacks, so you need Simon and Carina to heal while Hilstara keeps up the buff.
But of course the third member has to be Varia, so that she can stab destiny at its neck like a horse.
In general the strat is to keep up double defense buff, take the boss to the second phase, use poison, and then turtle.