His father is George W on the marriage cert but as he is another Lighthouse Keeper it's difficult to know where he is from or where his children were born, not that John G would have a birth cert but a parish record is possible.
His marriage might have a cert, COI marriages were registered from 1845 but the images aren't online yet and couples that early are not matched up on the index yet.
Did you look at the Robert John cert 1914?