County Cavan Rusk Ancestors

My name is Hal Rusk from Des Moines, Iowa USA and I am search for additional information for Rusk ancesters. I have used Family Search and Ancestry and established very basic and limited information on my great grandfather, his brother and a sister. I know they came from Cavan county. They immigrated from Ireland to the US at different times and first settled in New York state. They all eventually ended up in south Iowa.

My great grandfather James Henry Rusk was born in 1820 and arrived in the US in 1847. He married Ann McQuaid in September 1945. She later died and he married Margaret Ray (1842-1932).

His sister Eliza Rusk was born in 1824 and I do not know when she immigrated. She married a Kelly in the US.

His brother Robert Rusk was born in 1836. I do not know when he immigrated. 

Thank you in advance for any assistance

Hal Rusk