First Earl of Roscommon

Can you or any of your correspondents put me on any plan by which I may obtain some information on the following subject? James Dillon, first Earl of Roscommon, married Helen, daughter of Sir Christopher Barnwell, by whom he had seven sons and six daughters; their names were Robert, Lucas, Thomas, Christopher, George, John, Patrick. Robert succeeded his father in 1641, and of his descendants and those of Lucas and Patrick I have some accounts; but what I want to know is, who are the descendants of Thomas (particularly), or of any of the other three sons? Lodge, in his *Peerage*, very kindly ki…