Hi Edward it might be worth following Bridget and Cecilia through all the American records as that may well provide you with their parents names, via obituaries, family histories, or naturalisation papers. It might also be worth looking for their American wills which may be online, just in case they mention anyone back home in Ireland.
I notice William’s death certificate in Pennsylvania is attached to one of the trees on Ancestry and has the same name for his parents, his death was registered in Connellsville, Fayette, by someone sharing the same surname so possibly a family member although the name is now spelt Roland.
Although he would have been well established by the time the Catholic Order of Forresters set up their life insurance scheme in 1879, as you can check their database for free it may be worth a quick look. Some of their records can be really detailed. See more on these records here http://tiara.ie/forest.php
I would also be inclined to post your query on the Mayo genealogy page on Facebook in the hope of coming across others researching this family. Then I would also post the query on the message area of the relevant parishes on Ireland Reaching Out, this again may in time result in making connections with others researching the same families who may have information different to yours.
Another place to consider leaving a footprint would be via a free account on www.curiousfox.com leaving a message with the heading Rowland in that part of Mayo.