It is likely that a John and a James Donnellan found in the records of Milltown Malbay, County Clare^[72] were uncles of Michael. Any of their children would have then been Michael’s cousins. They provide us with a large list of names and dates that can be used to identify living relatives, though such relatives would be distant (third cousins of Michael's grandchildren).

The descendants of Michael’s siblings would be closer than those of his uncles, but they may be harder to find and identify. We know the names of his sisters Alice and Ellen. It has been said that Michael immigrated to America with a brother and two sisters. Were the sisters Alice and Ellen? Those two would have been very young at the time, but possibly old enough to emigrate under the care of their brother(s). We may soon know that Michael had a brother named James who immigrated to America. If we can determine the name of Michael’s brother, presuming such a brother ever came to America, that brother would probably be much easier to track than Michael’s sisters.

Michael may have had a half-brother named Patrick. It is interesting that his father and mother didn’t have any baptisms recorded after 1849, but then a Patrick Donnellan had a child named Patrick with a wife named Bridget in 1853. This Patrick, like Alice and Ellen, would have been too young to emigrate on his own in 1861, but he may have possibly gone under Michael’s care. However, there was ample time between Michael’s birth and 1846 for several brothers and sisters to be born – not to mention the years immediately before Michael’s birth.