That's right, the money legally belongs to the child who inherited it. The only person who has the legal ability to decide to use the money for someone else's benefit is the child who inherited the money, and the child won't have the legal capacity to do that until the child reaches the age of majority. Until that happens, the account will be under the control of a custodian, who is under a fiduciary obligation to use the money only for the benefit of the child who inherited it.
It shouldn't be possible in any circumstances; doing so would be theft. Each brother can have full control of the money once they reach the age of majority as prescribed by the applicable state laws. Once they reach that age, they may choose to give some or all of their inheritance to their brother, or anyone else for that matter. But nobody else can make that decision for them.
The money belongs to the brother that inherited it, and should only be used for that brother's benefit until the brother reaches the age of majority and decides otherwise.