>The Machiguenga had traditionally been horticulturalists who lived in single-family, thatch-roofed houses in small hamlets composed of clusters of extended families.
Their living situation is one where they are all essentially family. There would be big social impacts on costing your family money, because of some perceived issue with an unequal split.
They are likely all going to spend 'together' anyway. They are probably bewildered why this weird foreigner doesn't grasp this basic fact, and is forcing them to go through some bizarre ceremony to get the money.