What rubbish. This is one of those urban myths that do the rounds from time to time. Feargal Sharkey is a working class lad from a housing estate in Londonderry. Eamonn Andrews was from Dublin and to my knowledge never met Feargal's Mum, much less fathered a child by her.
Think not. Eamonn Andrews does indeed have a son and he used to play bass with the now (unfortunately) defunct Cactus World News who were one of the best Irish Rock bands ever.