Hi,
Thank you for your message.
Given that both Walter and William listed the exact same parents? names on their marriage certificate I think that the possibility of them being brothers is very strong.
However, you could try looking in church records in the parish to see if you can prove the connection. If you can find a birth record that shows William was born in Clonfeacle also I think that i would be sufficient proof.
Most Catholic records are held locally so you may need to write to the local parish priest for possible assistance. One website that you may find useful is the Irish Times where they give an overview of what records are available in specific parishes. It also shows you where copies of the records are available. For Clonfeacle parish, follow this link:
http://www.irishtimes.com/ancestor/fuses/rcparishmaps/index.cfm?fuseaction=showidrecords&CityCounty=Armagh&parish=Clonfeacle&churchid=199
Most surviving Church of Ireland records are still held by the local clergy, although some are in the National Archives of Ireland and others are in the Representative Church Body Library in Dublin. Here are their websites: http://www.nationalarchives.ie/ and http://ireland.anglican.org/about/42
Lists of these surviving registers can also be found at the National Library of Ireland.
Unfortunately, no census records from the period survive to show all four of them in the same household so I think church records may be your best option.
Alternatively you could contact Armagh Ancestry for assistance, however a fee may apply. Here is their email: researcher@armagh.gov.uk
Please be patient - as our programme has only begun to rollout across the island of Ireland and volunteers in some areas may not yet be organized.
Kind regards,
Genealogy Support