Bourkes of Bruff

I hope one of your kind experts might be able to help me to find my great great grandparents John Bourke and Mary Ellen Bourke (née Dundon/Dunden).  Their son William Joseph claimed on his marriage certificate that he was born in London in 1851 and that his father John was a saddler.  But William’s death certificate says that he was born in Bruff. William didn’t name his eldest son. ”John” after his father in the traditional way, but instead called him Walter Henry Edmond Bourke. Other sons were given very English names: Percy, Norman, Cecil.  It’s a bit of a mystery. William came to Australia in the mid 1860s. Does anyone know of a John Bourke and Mary Ellen Dunden in the Bruff area? Many thanks in advance. Paula