Show all systemd services which are enabled, but not running

I think you need to add an After= clause. If your three services are linked, you might also be able to simplify your Requires.

If you also wanted this fourth service to stop when the other 3 do, you would also need to add a BindsTo entry.

As in:

[Unit]
Description=This is the group
Requires=c.service
After=c.service
BindsTo=c.service

You control the shutdown order by specifying Before= and After= in the unit files to describe the startup order. The inverse order is applied when shutting down.

Here's what the official docs have to say about it:

...when two units with an ordering dependency between them are shut down, the inverse of the start-up order is applied. i.e. if a unit is configured with After= on another unit, the former is stopped before the latter if both are shut down...