They don't know if they have Peter's bones. I saw a tour of the Vatican on the History Channel. It was interesting b/c low level priests would keep referring to the Vatican treasures as the bones of Peter, Veronica's x, Mark's z. Cardinals, however, kept talking to the documentary crew in terms such as "bones dating back to the first century that legend attributes to Peter."
I am disappointed in Francis. One of the Vatican treasures I saw when I visited was St. Helena's stairs. They are supposedly (a big supposedly) stairs that Jesus walked during the Passion. They are hard stone. Poor, old peasant women, dressed in black,, were kneeling on them and reciting rosaries. No man did the stairs. No person below 70.
How do Peter's bones promote spirituality or belief? Many scholars doubt that Peter was ever in Rome.