How do you beat the golem sisters on chrono trigger?

The Golem Sisters will counter all physicals with Iron Ball (Cuts HP in half) and all magic attacks with magic of the same element that hits all. If you were smart or read a walkthrough you should have got both the White Vest and White Mail. Equip each one on a member of your team. Give the last person something that resists magic and enter battle. In battle, use Crono to spam Luminaire while the other two support (Haste, Protect, healing, restore MP etc.) The Golems will keep countering with a Light-based tech that heals 2/3 of your team. If you keep up on the healing the Golems will die pretty fast cos they only got around 7k HP and Luminaire should do 1k+ per turn.

If you don't have Luminaire, then put frog and marle on your team + one more support. Equip Blue Vest and Blue Mail instead. Get Frog and Marle to blast away with their best Water magic (Water II, Ice II, Glacial Freeze etc.)

In fact this strategy will work with any elemental attacks as long as the correct armor is equipped.