Lord John Bateman in 1840s?

My 3rd cousin made a previous post (titled O'Kief/Bateman) looking for information on our mutual ancestors John O'Keeffe/Keefe and his wife Mary Bateman. As a quick recap, John O'Keeffe worked as a hostler for a man named Lord Bateman. John fell in love with Lord Bateman's daughter, Mary. We think maybe Mary's father was against the match so they ran away to the US along with Mary's younger sister, Susan, and lived on a farm in Wisconsin until their deaths. 

At the time of my cousin's post last year, we had no information on John or Mary's parents' names. All we knew was that John O'Keefe was from Cork. I have been able to find death certificates for both of them. John's father's name is listed as 'John Keefe/Ireland' but there is no information on his mother's name. Mary's birthplace just says 'Ireland', her father's name was John Bateman and her mother's name was Catherine. It says both her parents were from Ireland.

I thought finally having both parents names would open some magical door, but I am still stuck. Every cousin I have managed to make contact with has been given some version of the story that 'Lady Mary Bateman ran off with the lackey/gardener who worked for her father Lord Bateman and that she and Susan were disowned.' I have had DNA done for myself, mother, and my great aunt Jan- Mary Bateman's great granddaughter. We are getting many high confidence Bateman DNA matches to people with Bateman ancestors with ties to Cork Ireland. If Mary's father John Bateman was indeed a Lord at the time she sailed (1848) shouldn't he atleast be easier to find? I've seen many John Bateman's in Griffith's but how would I know if they were a Lord or not? 

Does anyone have any advice or know where I should be looking? I'd just love to know where Mary and her parents were from, if she had other siblings besides Susan, and possibly go a little further back in the tree.

Here is what I know about Mary: b.6thAug1824 Ireland, dau of Lord John and Catherine Bateman, has a sister Susan b.1826, possibly Protestant but definitely not Catholic, left Liverpool on the ship Westpointe and arrived in New York 3rdJul1848, husband was John O'Keeffe/Keefe b.24thAug1818 Cork, Ireland-Catholic, place of marriage unknown, she died 8thAug1907 in Poygan, Wi from an aneurysm.