I had 2 ducks sharing a nest and they did come out during the day until they thought they had enough eggs then sat side by side on two nests. When one got up for a walk the other would move one or two eggs into her nest, but sometimes you would find them swapping nests. If one got off the other would move to her nest but they seemed ok with this system. They hatched 20 ducklings between them and l thought one would steel all the babies and keep them for her own but they are both looking after the little ones and share babysitting duties if one wants a bath. One of the ducks is the dominant one and if she does not get her bath she can be a bit bossy but usually they get on and are not aggressive. They are muscovy. I was told to let them get on with it and thats what l did, they seem to know what they are doing. We have 20 ducklings now.