The answer lies with the parents. Do they migrate or do they stay in your pond year round? Does your pond freeze? If migration and pond freeze occurs, then there is a greater chance that the parents will tell the cygnets it is time to go and will show them how to leave. This should occur within the next few weeks. However, it depends totally on the cygnets if they choose to stay together or go out and find another swan to pair up. Yes, swans will and can interbreed with family members, but unlike mammals, there is minimal problems with genetic anomalies. The Regal Swan