Of course you must have a local network to which all RasPis are connected. WLAN is OK for showing pictures and stream audio files, but for video streaming it is limited, so you may consider to use wired connections for higher resolutions.
As already noted in the question you have three components:
the media server should run on a recent Raspberry Pi. It ...
You can use minidlna, a lightweight UPnP/DLNA server that fits very well into an environment for multiroom media, made with Raspberry Pis. It is available from the default Raspberry Pi OS repository. Just install it with:
rpi ~$ sudo apt install minidlna
It is working out of the box with default settings. Copy some media files to `/var/lib/minidlna/' and ...
Looks like for the time being this package has to be installed manually
I was able to get it working (not using raspivid) after installing the package manually.
gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0
After I ran this, I was able to open the ...