回複：Do you read?

I read the entire I-864 form. I also asked a lawyer about the form and was told I could fill the part 3 for my sister's family.

The instruction on the form is

The immigrant you are sponsoring may be bringing a spouseand/or children to the United States. If the spouse and/orchildren will be traveling with the immigrant, or within sixmonths of the immigrant's entry to the United States and youare sponsoring them, you should list the names and otherrequested information on the lines provided. If anydependents are not immigrating, will be immigrating morethan 6 months after the sponsored alien arrives in the UnitedStates, or you are not sponsoring them, do not list their nameshere. A separate Form I-864 will be required for them whenthey apply for their immigrant visas.

The box 8 is
I am sponsoring the principal immigrant named in Part 2 above.

The box 9 is
I am sponsoring the following family members immigrating at the same time or within six months of the principalimmigrant named in Part 2 above.

It seems I can sponsor my sister's family. Anyway, her famliy can come to USA at the same time when she comes.

Thank you for your help.