I’ve been extremely impressed with the XIAO and have gravitated toward it for any non-networked microcontroller project of late. It’s easy to integrate into the Arduino IDE (ptooey!) or PlatformIO (much better!).
You should probably include LIDAR altitude sensing in your drones if you haven’t already. An absolute, accurate altitude reference will likely prove invaluable in swarm operations. You could determine threshold altitudes for flip/avoidance maneuvers for self-preservation.