I can't help with the wife of Denis or any records for Denis. However, I did locate a death record on the subscription site Roots Ireland for a Peter Kean who died at age 75 on December 30 1849 at Rathowen (Rathaspick) RC parish. No location is listed but i suspect he may be the father of Denis. Also, in the 1854 Griffiths Valuation head of household listing for Rathaspick civil parish, there is an Anne Kane listed in Henfield townland https://www.failteromhat.com/griffiths/westmeath/rathaspick.php Likely she was the widow of Peter and at some point Denis took over.
This may be Anne's death record in 1887 next to last record
FYI Look at the last record on the page for another Anne who was part of the Stongaluggaun Keane family.