Broadcast Message to multiple groups

[jamesonuk]

Thanks to the previous occupants, most the rooms in our house have multiple downlights for which I have a group per room.
This works great for almost everything but I have one use case that doesn't work...

I have an automation in HA that when no-one is home is arms the alarm and turns all the lights off. This however generates individual MQTT messages for each group (plus a handful of other individual lights). Trying to send that all at once floods the network and only some of the lights actually get turned off.

Is it possible in Zigbee to send out a broadcast message that is for multiple devices? Thinking that if I could send one broadcast message that included all the groups I want to turn off this should prevent the flooding and actually work? If this would work, how could I create that message in Z2M?

Or are there any other solutions? The only thing I have thought about is having the individual bulbs in multiple groups (which I think is possible?) and have one massive group for all lights. This isn't ideal as then I need to maintain two groups and I am not sure if there is any issues with a huge group containing something like 50/60 bulbs?