You have to fill I-134, Affidavit of support form, if you need to show that you can financially support your relatives (or anyone else) visiting the U.S. You do not have to get it notarized anymore.

Fillable I-134, Affidavit of support

Sample I-134 form and instructions

1. Print it on 1 page on 2 sides. Do not print on 2 pages. If you don't have a printer that prints on 2 sides, first print on 2 pages and then make 1-->2 photocopy.
   
   
2. This form no longer needs to be notarized by a U.S. notary.
   
   
3. Many people ask whether the sponsor would be liable for any medical expenses that the visitor medical insurance may not cover because of pre-existing conditions. There is no clear answer for that. We have never heard of USCIS going after a sponsor for unpaid medical expenses and collecting expenses from a sponsor. Many lawyers think that I-134 is a flawed legal document and would not hold up in court. At the same time, there is no guarantee that USCIS will never go after the sponsor to collect the money, especially the money that the U.S. government might have spent on their behalf.
   
   It is also not very clear how the hospital would come to know that you have sponsored the visitor and therefore, hold you liable for expenses. It is not clear how USCIS, Dept. of State and the hospital will work in sync to find all these out. If you have signed any documents in the hospital stating that you will be responsible for the payments on behalf of the visitor, the hospital will definitely hold you liable to pay. But otherwise, it is not clear what exactly will happen.
   
   
4. If both husband and wife are working, both can combine their incomes/savings and put a joint amount in one form.
   If the wife is working, and wants to invite her parents, it is better that she is the sponsor and not her husband (A parental relationship is closer than an in-law one). In that case also, you can still put joint income.