Lynne,
Still cannot find any baptismal records for my Richard Kilroe, but based on several DNA matches that I have with descendants of Peter and Esther Kilroe as well as a match they have to another of my 3rd cousins who share the same lineage I am pretty sure Richard somehow belongs in this family group. It seems likely that he may be the brother of Peter Kilroe’s father, Michael Kilroe, who you have being born 1821-1831. Richard was probably born around 1817-1820. Info on death records is always so iffy, but the name Michael does appear on Richard’s DC and so your thoughts on Michael Kilroe and M Brennan would fit. The sister to the 3rd cousin I mentioned above also matches some Kilroes who immigrated to Canada about the 1840s. This couple was Lawrence Kilroe born 1782 and his wife Mary Dunn 1788. They had children John 1817, Bridget 1820, Michael 1821, Catherine 1823, Stephen 1827, Mary 1831 and Ann 1832. They all lived in Nepean, Ottowa, Ontario, Canada. Although Richard was reportedly born in Kings County he seems to also be connected to Westmeath since his first marriage took place in Moate. On the other hand some of the children of the Laurence mentioned were born in Tipperary and Limerick, so perhaps the family had been moving around and records are farther afield than Kings! Will keep digging and let you know if I find anything.
Eileen