Gold without proof of origin as an inheritance/donation

I'm currently dealing with the following scenario, perhaps the swarm of knowledge can help with input: Mother (70) would like to pass on an early inheritance/gift to her two children. Child 1 is to receive a property worth €160k. Of course, child 2 shouldn't go away empty-handed and would therefore receive around €75k in cash and 700g of fine gold (7 bars of 100g each). Problem: There is no proof of origin for the gold. Ultimately, it was mostly inherited from the grandmother, however