If you are sponsoring your family to come and live in the US, you will need to file a Form I-864 (Affidavit of Support). USCIS Form I 864 serves several very important functions. First, it helps prove to the USCIS that you have the financial means to support your family members once they are in the US, so that they do not become a burden on the US benefits system. The affidavit also shows your willingness to support your family members while they are in the US.
If you are sponsoring relatives for a green card, it is important to keep in mind that filing an Affidavit of Support does place you under some legal obligations. In fact, this immigration form is considered a legally binding contract between the U.S. Government and yourself. The form is used to show that you have enough income to support yourself and your sponsored relatives at 125% above the Federal Poverty Guidelines. By signing the form you also agree that your assets and income can be available to support your sponsored family. In addition, by filing the USCIS form, you agree to accept legal responsibility to support your sponsored family. If you do not offer this support, Form I-864 means that your sponsored relative can pursue the support through legal means (such as a lawsuit). If you do not provide adequate support for a sponsored relative and that relative needs to rely on means-tested public benefits from the US, your obligation under Form I-864 (Affidavit of Support) requires you to repay the benefits to the agency that offered them. The government agency can even pursue the debt through legal action.
Your duties continue until your sponsored relative either becomes a US citizen or works a prescribed period of time in the US (usually 10 years). Your obligation will also end if your relative passes away or leaves the US and abandons his or her green card status.