This article is from the Final-Fantasy and other Square Soft Games FAQ, by firstname.lastname@example.org (Nick Zitzmann) with numerous contributions by others.
This doesn't seem very obvious at first. However, the Golem Twins copy
whatever attack you might use against them. Your character's physical
attack, unfortunately, is their strongest copycat attack.
Refrain from physical attacks at all times while fighting, and
concentrate on high-powered magic attacks. Try this: Take Lucca with
you; equip her with the Taban Suit and equip the others with either Red
Vests, Red Mail, or Ruby Suits. Have Lucca cast Flare, and the other
characters hang tight and restore Lucca's MP. The fire copycat attacks
used by the Golem Twins will have little/no effect against the Taban
Suit and Ruby Suits, and will be absorbed by the Red Vests and Red Mail.