What happened at the “end of the 1800s” won’t explain what happened to the family between 1840 and 1860. And, the family’s wool-income increased from international sales, so general prices increasing faster than domestic wool prices increased has no impact.

The family’s wool-income increased due to greater international sales. Even if the family made less wool-income from domestic sales, we already know their overall wool-income increased because of international sales.

If prices for these non-wool products sold by the family fell sharply, that could have offset the increased income from wool-sales. This shows why overall income for the family might not have increased, even if wool-income did.

Even if Australian wool producers in general were in a less favorable position than previously, we already know this family increased their wool-income. This answer doesn’t suggest why the family’s prosperity might not have increased along with their wool-income.

We already know this family increased its wool-income from international sales. Whether other farmers exclusively sold internationally doesn’t tell us why this particular family might not have seen an increase in prosperity along with its increase in wool-income.