It turns out that two of the geese are female. I was told that geese don't have a great hatch rate so I left the majority of the eggs with them. As a result they proved everyone wrong and hatched 19 goslings ! Two died in the first day, the rest have made it to full feathering.
As goslings they were adorable fuzzballs that wee-wee'd their way around the farm under the watchful eyes of their parents.
Geese are grass eaters, like sheep. I feed the flock a couple of cups of soaked grain each evening to help them stay warm in cooler weather. In the meantime the goslings grazed with their parents and grew like the proverbial weeds.
As crossbreds it's impossible to know for sure what the gender of each goose is until they start laying eggs and sitting on the nest. The aim is to have two or three pairs. I'm going to keep the original three adults and another three young ones. We could end up with any combination, but hopefully at least enough of each gender to form a stable flock.