Sponsor Document for Visitor Visa B2

[immihelp]

Hi,
I have already sponsored my parents & in-laws & successfully got their visitor visa.

Now I am going to sponsor my
1) Real brother
2) His wife
3) First kids (6 years older)
4) Second kids (2 years older)


My question is:

1) How many "I-134 (affidavit of support)" is required? (Do I need even for the 2 minor kids also?)
2) How many "Employment Letter" is required?
3) How many "Letter to Consulate" is required?
4) How many "Invitation Letter" is required?

[immihelp]

One is enough.