So all of the machines are connected to the hotspot network hosted by one of the Pi’s? If so, edit these files on it:
/etc/dnsmasq.d/wifi-hotspot.conf/usr/local/pisound/scripts/pisound-btn/enable_wifi_hotspot.sh
Set the IP values and ranges as you like.
See my reply here on how to assign fixed addresses to your other devices: FAQs - Pisound Docs