My dad raises domestic geese on his farm. Many times they will lay their eggs in one or two community nests. Then, when the goose decides to sit, she may be sitting on her eggs as well as her neighbor's eggs. When the chicks hatch, they stick with the 'mother' who hatched them. I don't know if it works the same for non-domestic geese, but it makes sense.
Lovely photos!
Cheers,
BD