How do abilities which trigger "after actions resolve" work with things like multiattack/working together/multiple mind control?

For instance

If my opponent uses working together with a 300 pt team base, and makes an attack as a free action.

Do they take 1 unavoidable after THAT action resolves, or after the Working Together resolves entirely?

I feel like since the triggering action was the free action, it should be triggering after the free action, not waiting until the power action finishes.

Is this correct?

It means after all current actions have been resolved. If there is an action that isn't yet resolved like Working Together, you will have to wait until that action has also resolved.