Toggle a group of lights in automation - with brightness

Hi, I have a zigbee switch and I’ve created a group of lights (from helpers):
Group name: Dining Room Lights
Entity name: light.dining_room_lights

I’m using tapo bulbs in a 3 way light (can’t change as we’re renting). The brightness of all 3 bulbs needs to be 20% each

How do I make a toggle automation for these lights to turn on/off at the touch of the switch? (I know how to make regular automations)