There are two ways to set up a parent/child relationship between the rows in a NotesView. First works with one or more types of documents where you take a flat view of documents, pick a column to group by, and set its type to Categorized. The Category row then shows up above the entries that have their field set to the category value.
The second way is to have two types of documents using the built in document / response (and optionally response to response) relationship. In your form selection criteria, you make sure you select all the documents you want, and then tack on the descendants. In the view settings you need to select "Show response documents in a hierarchy". Then the parent documents will show above all their child documents.
I think you're trying to use the second method, but it seems like something is missing. When it is set up, the parent row can show any number of columns, and usually the child row shows only one (see the design of the built-in discussion databases). To designate a column to be for responses, select the Show Responses Only option in the column properties. Otherwise the column will appear for just the parent document.
To get what you want to do you should just need a couple of columns. The first one would be for the response documents and can be very narrow, but will automatically stretch across the whole window. The second would be for the parent document. Lastly you can select the "Extend last column to window width" option so the parent column fills the screen, or just stretch the parent's column wide enough to fit everything. You can even set the view properties to allow that column to show on multiple lines (up to 9) if it doesn't fit on one.
Hopefully this fills in any gaps. If I missed something please let me know in the comments.