A Connection between the Cahalan and Darcy families?

Hello everyone!

My great grandmother, Mary Darcy, was born in Terryglass in 1846 and emigrated to Australia in 1866. Her passage was sponsored by my great grandfather John Smith from Abbeville, Lorrha who'd made the move to New South Wales some 18 months before hand. His passage was sponsored by a Michael Calahan, also leaving from Abbeville, who'd left for Australia in 1863.

Now it is my belief that there is some connection  between the Cahalan and Darcy families which I'm slowly unravelling. 

Mary's father was James Darcy and his father was William Darcy. Michael Cahalan had an older brother James and his father was also a Michael.

In the 1847 Terryglass Rate Book, a James Cahalan and William Darcy are sharing a property at Drominagh (Dromena in the rates book) and I'm almost certain that this James Cahalan is the father of Michael, the grandfather of Michael Jr.

My question is: Considering the timing of 1847 in relation to the Great Famine, were James Cahalan and William Darcy (and I'm almost certain probably thier families which at the time would have included my great grandmother) co-tenants of the property at Drominagh because they were somehow related or was it just that they knew each other?

The Cahalan family made a mass move to Australia in the early 1860's and my great grandparents followed so I'm wondering how the Cahalans fit into my family tree... if at all!

Cheers,

Mario