Are you referring to the one with the 3 Mieshas? I can't remember exactly what i did since its been quite a while (i did just kill them on NG+ Extra though , a bit of a joke with some of the skills i get to keep
) . I do recall it being rather tough first time through.
IIRC , you need to get rid of one Miesha at a time (ie: kill one per turn) or else they'll just heal and you are fucked. Build on SP (via item spam, buff spam, death spam , etc) on a character, unleash your combos then finish off with the EX attack. Repeat till all Mishas are dead. Then kill the golems.
EDIT : I AM ANNOYED.
Started with Battle Mage Sword/Daggers Sieg. Now at Max Affection and at end of Gen 1, i have the following options.
Str/Vit/Agi/Int/Luk
Leonis 1 (Linda) : A/A/B/B/C (Daggers)
Lenos 2 (Routier) : C/C/B/S/D (Fists)
Leonis 3 (Sayane) : C/B/B/A/S (Swords/Daggers).
Basically i already went with Linda on first playthrough and wanted to pick another ==. The only issue is that the other 2 options are just bleh. I want a battle-mage and the only one i can pick is Sayane which has C for STR (wanted B at minimum). Really hate the stat unpredictability of the system -_-;.