Affidavit to be prepared by parents

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Hi,

I am applying for visitor visa for my parents.
Apart from the affidavit of support prepared by me(sponsor I-134), do my parents also have to prepare an affidavit indicating their property and nature of visit and family ties?

Is their any specific format for that? If yes can anyone provide me that?
My parents are going together on the same day for the interview. Do they have to prepare separate affidavit?

Also I have a younger married brother staying with my parents in India. Is it fine to mention him in the affidavit?

Any help will be greatly appreciated.

Thanks in advance.