With the whole chain, not the final balance. The succession agreement, the independent valuation, the cooperative’s redemption of his interest, the notarial records, the tax returns reporting each step and dated statements for every account the money passed through are what answer the source and path questions together.
Every hop needs a document and a date
Family transactions are documented for family reasons, which are rarely the reasons an adjudicator has. A verbal understanding that the parents would release a sum once the transfer completed is real to everyone involved and invisible on paper. The remedy is to convert each understanding into a record while the people who remember it are available: the written agreement itself, the valuation that set the numbers, the resolution by which the cooperative redeemed the interest, and correspondence with the notary.
Then follow the money forward. If the funds sat in a parent’s account for a month because that was where the cooperative sent them, that month needs a statement and an explanation. If a currency conversion took place, the institution and the rate belong in the file.
Documents not in English require complete certified translations. A chain assembled contemporaneously is straightforward; the same chain reconstructed two years later is expensive and sometimes impossible.