The lone swan could be a juvenile kicked out of the habitat by the parent for the upcoming breeding season. He/she at least has some waterfowl pals to hang around with until the migratory season when the swan will leave and then try to find a lifelong mate. The only other explanation is that something happened to the parents and the swan has found your area as a safe habitat. In NJ and other areas, state and wildlife officials kill Mute Swans (both adults and juveniles) under the misrepresentation of the Mute Swans being aggressive, displace other waterfowl/wildlife, eat too much aquatic vegetation and are non-native. All total falsehoods as the reasoning is to remove the Mute Swans from wetland habitats so that the larger Trumpeter Swans can be introduced for Trophy Waterfowl hunting. Hopefully, this is not the case with your swan.

As far as the goose, the goose may be a relative to some in the flock and therefore, is accepted. Because it looks different, the others may not see it as a potential breeding conflict with the other members. There are many anecdotal stories of various species adopting, allowing the adoption or care giving of their young by other adults of the same species. This may certainly be the case of the goose. The other flock members do not see her as a threat and because she may not be able to have her own brood, has accepted the position of caring for the younger geese. Some geese and ducks will readily adopt young from another parent if something happens to the parent. This is an individual attribute as there are just as many that will not accept another's young. The Regal Swan