I think it unlikely that you are descended from RRG. In my experience, all Irish Gillespie families (including my own until my father researched his ancestry) believe they are. RRG had no legitimate children but two illegitimate - Selina (by Mlle D'Oboreuf) and Robert Rollo (by Melle Pécher). Selina married Andrew Carew O'Dwyer and their daughter Mary married Timothy O'Brien, younger son of Sir Timothy O'Brien Bt, the first Catholic Lord Mayor of Dublin. From this marriage the O'Brien baronets descend and the head of the family is Sir Timothy O'Brien 7th baronet, born in 1959. They are not related to the Inchiquin O'Briens. Robert Rollo married three times and only had children by his third wife, Sally Maria Blaxland - another Robert Rollo, William Augustus and Caroline. This RRG had two sons and four daughters; the sons were yet another Robert Rollo (who had no children) and Jack (a captain in the DLI) who had only one daughter, so the Gillespie line died out here. But William Augustus had two sons, one of whom died in infancy and the other, Robert William, had a son, unsurprisingly Robert Rollo 1990-c 1986, a captain in the RE, from whom two more Robert Rollos descend, the last being Rowlie who contributes to this thread. There are no Henry John Gillespies in the tree, so like me you seem to be from a parallel line of the same name.