回复：请教懂法律的朋友，老猫等朋友

Based on the fact you stated in above, all of the sons of the parents are entitled to the 300,000 dollars.

First of all, he gave his parents the money as a gift. After the transaction, the money belongs to the parents. Then, the parents asked him as an agent to buy a house for them, so the money is not a gift to him.

But because there is no written agreement, he might be able to argue that the $200,000 is a gift from his parents, even though it is not the fact.