unfortunately we don't have functionality to filter parent items by their tasks assigned to. If you consider this as disadvantage of our product you can submit a feature request in our Ideas & Feedback Portal
and give a vote up for it so we can move it faster in development. Our customers feedback is important to us so we can make our product better and easier of use.
Currently, you could add filter for parent items by their assigned to, using board row settings. Another option is to use My Perspective view, we designed it to display all your tasks, and each task shows information for its parent and also, you could easily navigate from the task to the parent.
I hope that was useful for you and apologize for the confusion.
If you have any other questions do not hesitate to contact us again.