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.
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 Apple, the Libyan state and the Aviva Stadium. Sales are thought to be north of €400m. O'Kane left €108,173,216 in his will after he died suddenly in 2007.