If I had the answer to your question, I would be a wealthy man. Cities throughout the world have the same problem you have, and spend much money trying to control pigeons, without much success. If you wait a few more days, the two youngsters will fly away from the nesting area. After that, I suggest that you put up a net or wire or cover the nesting ledge with something before the parents start a new brood. The point is to keep the pigeons from being able to land on the ledge.