Yes, it is possible that they may injure him or kill him. However, nature usually subscribes to the larger or stronger animal. The swan that is being beaten along with its family, will usually try to avoid the new rivals as much as possible. If you can possibly harass the new swans to the point that they leave the area, this may be the best solution. Again, nature will usually take its course and hopefully, the older pair will be smart enough to give the newer pair a wide berth until the new pair are harassed so much that they find this new habitat unacceptable to them. We hope this helps. The Regal Swan