Rosaleen O'Kane (70), her sons Eamonn and Ronan, and daughters Clodagh and Rachel, own around 70pc of Mercury Engineering, one of the country's largest private electrical engineering firms.
Headquartered in Dublin, it was set up by the late Frank O'Kane in 1972, and has worked on lucrative projects from Russia to the Gulf and the Corrib gas field. Clients have included Shell, Apple, HP, the Libyan state and the Aviva Stadium. Europe is currently the company's main focus. O'Kane left 108m in his will after he died suddenly in 2007.