There are no guarantees that the old swans will re-pair. Additionally, one of the new males could seriously hurt or kill the other male swan. It would be best to leave the two females together as they know each other and the habitat. Trying to introduce two new males will require two secured pens (1/2 In water and 1/2 on land with feeder in each. Both pens must be secure top to bottom so no predator can dig under or crawl into the pen). Both swans will need to stay in their pens for approximately two weeks to acclimate themselves to you, the habitat, the other swans and any predators (domestic or wild). Since you don't know what killed the other swans, you would not want to introduce other swans in the mix and have them predated because they aren't familiar with the surroundings and possibly roam in unsafe areas. Keeping any new bird or other wildlife in a pen for two weeks in this situation may also prove to be extremely unsafe. The two females will do just fine without a male mate. We hope this information is of benefit. The Regal Swan