Your challenge is to devise an inheritance system in which a minimum number of heirs is required for an inheritance to be legal. Specifically:
1. The minimum should be at least three, who should all be treated as an equal of the benefactor's son.
2. If there are less heirs available than the minimum number required, additional heirs shall be chosen, the process of which can vary, e.g. by serching the family tree, clan/church arbitration, or even given to charity. However, spouse(s), siblings, parents and *government should better not be eligible, as I want this kind of inheritance to work properly instead of being abused.
3. This method need not apply to the sovereign(if there is one), the poor nor the childless.
4. This method must be used in a country or at least a recognizable culture/religion (several million members if in modern times).
5. PoD can be anytime in the historical era, that is, no random appearance of a people using it since time immemorial.
My rational for it is for a certain society to prevent amassment of wealth through strategic marriages, entice wealthy people to procreate, and maybe, strengthening family bonds depending of implementation. But the result of what is presented could be very different from what I imagined, so please describe what such system does according to you?
* spending it on common good is okay.