Case: bring wife and kids

[Y268]

Hello
I am asking on behave of my friend.
One of my friend has green card and he is in the USA right now. His case in NVC to bring his two kids and his wife to the USA from abroad. His number still didn?t appear in the website visa and I think next month his number will be current.
They ask him about TAX document and he is doesn?t have guarantor. What he should do in this situation? Thank you.