DS-260, DS-261 quesitons!!

eagle2020

Registered Users (C)
For an immigrant visa processing, both the beneficiary(my brother) and the petitioner (my mother) are outside the US and internet connection is horrible where they live beside their inability to read and write English.Can I fill Ds-261(choice of an agent) on behalf of my brother? or does it have to be filled exclusively by my brother? Let's say I become my brother's agent, will I be able to fill DS-260 on his behalf too?
Thank you,
 
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