Duplicate Results In 2 Columns But Reversed

I have to write a query which extracts everyone from a table who has the same surname and forenames as someone else but different id's.

The query should have a surname column, a forenames column, and two id columns (from the person column of the table).

I need to avoid duplicates i.e. the first table id should only be returned in the first id column and not in the second - which is what i am getting at the mo.

This is what i have done

select first.surname, first.forenames, first.person, second.person
from shared.people first, shared.people second
where first.surname= second.surname
and first.forenames = second.forenames
and not first.person = second.person
order by first.surname, first.forenames

and i get results like this

Porter Sarah Victoria 9518823 9869770
Porter Sarah Victoria 9869770 9518823 - i.e. duplicates

cheers