I just read this post with great interest for there seems to be several prominent links with my family based on your post...even if they turn out to be cousins.
Though I have yet to find a Davitt connection to my direct y-line, my family did cross at one point with at least one Carroll, and we do trace back to Henaghan (Heneghan) in the early 1800. Also, my great grandmother was Catherine Rogan, born in Culleens, Ballina, Mayo, and she married Thomas P. Dougherty (Dogherty / Doherty) and he was from Ardnaree. Our Catherine Rogan was the daughter of Anthony Rogan & Sarah (Sally Ann) Brennan.
Anyhow...Catherine came to Philadelphia @1886 and married Thomas here. Some of the other Rogans, Walsh, Brennan and O'Hara relatives moved to the upstate area of Pennsylvania in the Winton / Scranton area.
Does any of this sound relevant to you and your family?
Thanks in Advance...Bill