@prologic@twtxt.net Here it is https://git.envs.net/cblte/docker-stuff/src/branch/main/syncthing.md have a look. This is how I have created the two syncthing containers.
Instead of mapping multiple volumnes, I have just mapped two locations where the actuall user (set by PUID and PGID) have read and write permission. This way they can write data and you can also access the data on the NAS itself, but limited to the individual user or admin, of course. Please let me know if you need any clarification.
One warning: when you disable global discovery, you have to set the IP of the devices manually on both sites. I was only able to get a connection doing it this way because of the non-standard ports.