The deed of sale and statement of adjustments, the registered title history back to the parents' acquisition, the marketing board's quota-transfer records, and the parents' tax returns showing the disposition and prior farm income.
Build the parents' trace exactly as if they were the investors
The gift moves the evidentiary burden one generation back. Start with the sale: the notarial deed and the statement of adjustments show the price and the net proceeds. Then the origin: the land registry's title history shows when the parents bought or inherited each parcel, and the earlier deed or the succession documents show that step.
Quota sold through the marketing board has its own transfer confirmation and payment record. The parents' income tax returns for the years around the sale show the disposition and, before it, decades of farm income, which explains the accumulation. Bank statements show the proceeds arriving in the parents' account and, later, the gift leaving it and arriving in the investor's account.
Add the gift deed and certified English translations of every French document. Write a dated narrative that walks through these records in order, and leave adjectives out of it.