The chances that the eggs are viable are very remote. Once an egg has been disturbed and not under the mom, even for a small amount of time, the eggs will not survive. Most of the time, swans will dump the eggs if there is something wrong. The birds know when something is wrong.

You can gently candle the eggs by placing a bright flashlight against the outside of the egg (as if you are looking into the egg with the flashlight on the opposite side). If you see liquid bubbles, no veins, then the eggs are not fertile. You will need to conduct this procedure in a very dark room, you will need to carefully handle the eggs so that you do not jiggle them and separate the cygnet from the egg. (This is why you must mark the eggs on the outside during the incubation process and slowly but gently rotate them so that each side of the egg gets warmed (just like the mother swan rotates the eggs).

In any case, we doubt that these are viable. If there are no veins and you see liquid, you need to take the eggs and throw them as far away from your house (preferably in the pond). These eggs can and will explode, can damage your house and they smell extremely rancid when they explode. You will be cleaning for some time.

If the eggs are solid, they may be viable, but less likely to survive. Should you successfully incubate the eggs, it is extremely important that you raise the cygnets with each other and possibly get them to a farm to be raised with other waterfowl such as ducks and geese. (YOU CANNOT return them to the parents as they parents will kill them).

If you do not raise them with other waterfowl, they will become imprinted on you, believe that they are humans and you will never be able to return them to a wild/semi wild setting because they cannot protect themselves from predators. This means they will always live in a VERY controlled setting such as a pen or fenced in pond. The Regal Swan