I would go HC12 if you want to keep a serial interface, super easy to set up transparent wireless broadcast
the NRF24s could easily be used too (mesh) - with their quirks as I find them sensitive to the quality of the power supply.
With HC-05 you could with a bit of work send a message to adjacent devices, just need to do that one by one and handle cases where a device is busy, retries etc. (There are AT commands to list all UUIDs. Of devices in range or this could be hard coded for each arduino if you want to limit the chatter)