ObjectUnsubscribedError when trying to prevent subscribing twice

Question

I have a Service and a component that uses it:

• PagesService
• PagesListComponent

In the PagesService

Answer 1

.subscribe() returns a Subscription

• You should use this to unsubscribe

e.g. Parent has a reloadSubject: Subject;

• child1 -> subscribes
• child2 -> subscribes

child1 - "WORKS" -> unsubscribe's his subscription

ngOnInit{ 
  sub: Subscription = parent.subscribe();
}
onDestroy{
  this.sub.unsubscribe();
}

child2 - "DOES NOT WORK" -> unsubscribe's the whole parent

ngOnInit{ 
  parent.subscribe();
}

onDestroy{
  parent.unsubscribe();
}

If you call unsubscribe on the parent both children are gone.
If you unsubscribe the Subscription that you get from the .subscribe() then only one child is unsubscribed.

Please correct me if I am wrong!