what are the obligations and commitments for the person who adds his income ..to support the petioners income
A co-sponsor has the same responsibilities as the principal sponsor. The form used is the I-864, and its instructions explain those responsibilities.
[This answer is for general purposes only and does not establish an attorney-client relationship.]
There is no form I-186 for immigration purposes.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.
I agree. Please contact an immigration attorney.