Hole in the ground hides Red-backed Fairy-wren nestlings

Here's the mystery. The nest hidden in long, thick dry grass is empty. But the Red-backed Fairy-wrens keep sneaking in with insects and leaving empty-billed.

Couldn't solve the poser yesterday. Put bit more thought into it overnight and searched more thoroughly this morn.

Found these two tucked into hole on ground close to deserted nest. One poser answered.
However, what happened to number three, or number four? Fairy-wrens don't usually do these things by twos.

As yet, no answer to that. There is a strong possibility, which remains unstated for now. Feel free to speculate.

Another question arises from the feeding pattern observed. Why should the female do almost all the catching?

Could it be because the male knows research shows that many clutches are multi-fathered?

Which means the male may be helping females at other nests. Which, in turn, possibly helps explain why fairy-wrens are so sociable and (though not in this instance) work in kinship teams to feed nestlings.