I don't have any more info on John Hickey & Margaret Cronin other than what you already have, but here is what is listed in our family records(Edmund Holland's sister is my gg grandmother) for their children:
Dorathea(Dolly), who married someone with the last name Jordan and they had a son Stephen
John 1812-1885 married a Johanna Driscoll 1809-1899
Mary married a Mooney and lived in Chicago, their children are Catherine & Nellie
Ellen (Nellie) 1809-1906, married Owen Hickey & later a John Hall
Elizabeth (Betty) married Patrick Haley
Catherine 1824-1911 married Edmund Holland 1816-1880
Below is what was written about Nellie:
Nellie Hickey, born 1809, died 19 Jul 1906, married Owen Hickey in Ireland. He died on shipboard coming from Ireland to America and was buried at sea. One son was sailing with him, Owen James Hickey, and was befriended by a family and was taken to the west. He is remembered as a young man coming to visit his mother. She was not allowed to sail from Ireland with her husband, for she has a baby in arms who was ill. She and her other children walked back to their home in Schull Parish, County Cork. The baby was dead when they reached home and it is believed the other children died. Nellie came to America in 1856 and married John Hall, who died 02 Mar 1889. A daughter, Mary Hall, died 30 Sep 1901, aged 64.
Based on the dates for the daughter Mary, I believe she is actually Owen's daughter & that John Hall adopted her when he married Nellie.
If you have gotten any further back since you posted this, please let me know. Thanks!