Sorry for the late reply. It is a bit complicated to make it work and getting the picking right is frustrating. But it is possible.
But as plinkie said, it is so much easier to just make different objects/families. It saves you a ton of time because it gets really complicated to pick between the same objects all the time.
I don't know if the plugin "nickname" is available for C3 but that plugin makes it possible to create objects by name which makes it super easy to spawn exactly the unit you want from a family.
But you can of course also just spawn the object you want instead of spawning a family. If you need to spawn a knight the just spawn the knight object.