Questions from a new chicken owner

For context chicken owner here with some questions. I have 3 chickens that just started laying in the last couple of weeks.

1. I have a hen that on three occasions now has gone into the nesting box in the morning for 20-30 minutes and came out singing but no egg to be found. Is this normal?
2. One or two of the chickens appear to be laying some soft and/or misshaped eggs. Normal?
3. Because of the soft eggs one of the chickens is eating them and now seems to stalk the girls when they go into their nesting box. Help!