The swans will get along with Dad up until about 6-8 months of age, then, he may start to chase them from the area because of the new mating season. However, since he does not have a mate, he may tolerate them a little longer. What is the size of your pond? Can it be fenced so that you can keep the two males away from the parent? You do not want to displace the male since this has been his home and it would be unfair to remove him. If you can fence the area to give the two cygnets an ample area and the male swan an ample area to bathe, preen, feed and swim, there should be no problem. Just watch for any signs of aggression. Try to keep the cygnets with the parent as long as possible as they need to know how to be swans. The Regal Swan