Help with Dempsey and Purcell and O Brien family

Hello,

Wondering does anyone have info to fill the gaps below. 

What i know

Daniel O Brien born and lived first part of his life in Churchtown Co Cork Ireland born around 1826 

Daniel Moved to Ballyshane Doneraile getting a farm in 1887. He may have moved to doneraile sooner and have been renting it. He got the farm from Matthew John Purcel of burton park Churchtown. 

He died around 1913

he had 3 children with Mary Dempsey. I not found marrage cert but i guessing they got married to have 3 children. 

Matthew John Purcel father John Purcell born 1801 married Anna Moore Dempsey in 14th may 1850. Anna father was the Daughter of M.K. Dempsey from kildare

So that what i Know. 

this is what i guessing 

Daniel married mary Dempsey, Daniel got land from matthew Purcel. matthew mother was Dempsey. 

So I guessing Daniel my G G Grand father married some relastion of The Dempsey / Purcell. 

As anyone come across the Purcell or Dempsey family tree and come acorss these names and dates