If you want to share an event with your brother that includes memories of your grandparent or family in general, consider the possibility of cycling where your ancestors came from or a place that has meaning in their lives. Last year I traveled to France to visit where one of my great uncles died during WWI. Since I was born 43 years after his death, I had never met him but his memory was kept alive in my grandparents' home along with the WW1 history of my grandfather and his brothers. I like to think that my grandfather would be happy to know that I went to see where my Uncle Eugene fought and died. Perhaps there is some place similar in your family history for you and your brother to cycle.
I hope you find a great place to ride and enjoy a wonderful time.