There are several approaches that you could use. If a field is preferable you should be able to use a calculation field and the List function. The field would be in your Owner table and would look something like List (Parcels::ParcelNumber) where ParcelNumber would be any field that you want displayed.
On your layout you'll either want the field to be large enough to display the maximum number of parcels you could expect for any single owner or possibly show the scroll bar on the side. If you don't do either of these you'll need to click in the field to see everything listed. If this is for printing I would recommend placing the field on the layout as a Merge Field and setting the text box to "Slide Up" and to "Reduce of the size of the enclosing part." You can then make the text box as large as you like, but once you switch to Preview Mode or go to print the page it will only use as much space as needed based on the length of the list for that Owner. Sliding and Visibility is under the position tab in the Inspector.
An alternative, generally the one I prefer for reports, is to create a sub-summary report. This would require creating a layout for the report based on your Parcels table. You can use FileMaker's layout wizard to create a first cut at a sub-summary layout for something like this and then modify it to fit any desired formatting. FileMaker's wizard will also create a basic script for running the report that you can also then modify to suit specific needs.
I hope this helps.