Margaret,
I am reviving this once more in case you are available.
When Frank and Mary Byrne left for America in 1883 under threat of arrest, they left their children behind in care of one of her sisters (I am searching for that source. It was in a newspaper. Probably London Times 1883). This presumably is the same sister who was interrogated by the British with Mary regarding the Cavendish murders. Immediately after this interrogation Mary fled to France to meet her husband. The (two) children in turn did not come over to NY until about 1886, after which there is a good trail. My confusion is that during the trial it was reported a few times (maybe incorrectly) that she was pregnant while carrying over the weapons used in the attack to Dublin. There are inconsistencies with this timing. I am wondering had you come upon a third child of Mary Byrne (Moneypenny) who appears in a sister's family inexplicably. Or was it another sister carrying child (Marcella would have been the likely in age)?
Many thanks for your time reading this. I have still not made the connection I thought would exist of Frank to Terence Byrne, the Fenian. I am however completely absorbed with what must have been a tough existence for the young family that Mary had to keep together.
Niall