Spreadsheet help with creating a formula?

Using OpenOffice Calc, I have a table with 5000 records. About 50% have the same last name and street address. I’d like to run a query that only shows one record if LN and address are the same, using the first name as the differentiator. There is also a unique key in each record.

For instance, if Tom Smith and Jane Smith live at 25 Anywhere Street, I want the query results to only show one Smith at 25 Anywhere Street, ideally concatenating the two first names into a new field; else deleting one of them.

Thoughts?