Thanks for your message and for sharing this information.
Have you tried looking in Church records for any information on Felix and Sarah? Perhaps if you can find their parents names, this will allow you to find the names of any siblings they may have had. If you trace these lines, through the Church records it might give you a better idea of who remained in the area.
Most Catholic records are held locally. One website which may be of help to you is the irishtimes. Here they give an overview of what records are available in specific parishes. For Kircubbin/Ardkeen parish follow this link:
Also, both Catholic and Church of Ireland records are currently being uploaded, free of charge, to www.irishgenealogy.ie/index.html However, this is an ongoing project so not all records are available yet.
You could also do a search for any family members in the two land records pertaining to Ireland in the 19th century:
The Tithe Applotment Books (1823-1838) found at http://titheapplotmentbooks.nationalarchives.ie/search/tab/home.jsp
Griffith's Valuation (1848-1864) found at http://www.askaboutireland.ie/griffith-valuation/
The last records that you can check online are the 1901/1911 census records. You can do this here:
Some other websites which may help you are:
The National Archives of Ireland http://www.nationalarchives.ie/genealogy1/genealogy-records/introduction/
The National Library of Ireland http://www.nli.ie/en/family-history-introduction.aspx
The National Archives UK ? genealogy search: http://www.nationalarchives.gov.uk/records/looking-for-person/
The Public Records Office of Northern Ireland http://www.proni.gov.uk/index/family_history.htm
Perhaps, you could also place this message in a local forum so that there is an even greater chance that someone will see it and recognise the names? Some places you could do this are:
The Down Recorder at http://www.thedownrecorder.co.uk/
The Down News at http://www.downnews.co.uk/
Alternatively, you could contact the Ulster Historical Foundation, however a fee may apply for their services. Here are their contact details:
Ulster Historical Foundation,
49 Malone Road,
Belfast BT9 6RY,
Phone: +44(0) 28 9066 1988 EMail: firstname.lastname@example.org
I hope that these suggestions help.