This is not the most humane way of taking care of cygnets. The best is placing the swans of the same gender on the ponds. However, if they can get back to the other ponds, they will try to find a mate of the opposite gender.

There is a gentleman that does take mute swans. Google: knox swans and talk to Bob. He can possibly help you out.

Yes, coyotes and other predators will eat the swans if they are not protected at night. This is also inhumane as swans in captive settings must be pinioned by state law (rendered unable to fly). So, the home owners are responsible for providing humane treatment and veterinary medical care for the swans. If they cannot, they need to place the swans in a better home.

Also, the females will sit on the eggs until they determine that there is nothing inside. By boiling the eggs, the female may feel something hard in the egg and thinks that she has a cygnet. But, if it does not hatch, she will eventually leave the nest. Also, the worst thing that can be done is to steal the eggs as females can count and will double clutch or try to replace the eggs which is not healthy. The Regal Swan