Answer has been solved but, just in case someone is curious about it: yes, is possible to extend a docker-compose.yaml file with another.

From Docker's docs: https://docs.docker.com/compose/multiple-compose-files/extends/

You can have a common-services.yml file (or whatever name you want to give to it) with a service defined inside, like this:

services:
  webapp:
    build: .
    ports:
      - "8000:8000"
    volumes:
      - "/data"

And then, in your docker-compose.yaml file just extend it with more specific things.

services:
  web:
    extends:
      file: common-services.yml
      service: webapp

You cannot reference a part of a docker-compose file from another, but you can have an .env file alongside them where you can declare variables in the format NAME=VALUE, and reference that in the dc files with ${NAME}, assuming your dc files reside alongside each other (with different names) and the .env file itself. I have done this before.

I cannot say if that will work for your use case, as I haven't tried to use the same docker volume in different containers. I don't even know if that is possible, given the possibility of conflicts if both containers tried to access the same files, something to test out, for sure.

Use a shared on-disk volume mount, i.e.:

volumes:
  - /data/docker/stuff:/whatever

In both compose files.

I use a similar mechanism to enable my media acquisition stack to grab completed files and store them in their permanent location.

Edit: you can just use the same volume in both containers at the same time, but you'd typically use an NFS mount or something if / when you try and scale this out. You probably just got the volume definition a little off (or need to create it outside both containers definitions and use it there)