how can I sponsor them to be here
You can send them an invitation letter and file for a Form I-134 Affidavit of Support, promising to cover theIr expenses while here, that could help if they are elderly and have no real income or properties to speak of in their home country. They will still have to overcome the INA Section 214(b) immigrant intent provision, but some US consulates are particularly deferential and respectful of elderly applicants, as they don't suspect they are coming to work..
If your parents are not already of retirement age it'll be harder for them to qualify for a visa, and the fact that their son or daughter was issued a visitor's visa and then managed to remain in the US through marriage or something else will not be helpful at all , unless one of them has a well paying job or business, properties and a good incentive to come back.
If you want them only to visit you, you can help them apply for the visitor visa by going to the website of US consulate nearest them in your home country and fill out the required applications.
As alluded to by Atty Behar, their challenge will be to show they do NOT intend to remain in the U.S. They should go to their interview with proofs of employment, property ownership, long-term lease, investment assets, etc - whatever they can to show they plan to return.
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