immigrant has only $280.USD income from pension
There are not near enough facts to understand what exactly you mean here. In terms of sponsorship, once a person has become a signatory sponsor (via I-864 or I-134) then they are legally liable against the non-citizen becoming a public charge. The sponsor does not necessarily have to give the non-citizen cash, but if the non-immigrant becomes a public charge then the U.S. government can sue the sponsor for the debts owed to the government by the non-citizen. A public charge ground is also a ground of inadmissibility. Beyond this I am unsure what you mean.
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You need to contact the local legal services provider in your area - Community Legal Services of Mid Florida - and ask for an intake to determien if you qualify for their services. The whole issue of support can be examined by an advocate with that legal services agency.
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.
Since this is a tax question, I am assuming you are asking if he needs to file his taxes. If he makes less than roughly $9,000 per year, he does not need to file. If this is his weekly or bi-weekly pay, he needs to file. If this is his annual or monthly pay, he does not.