My parents are both 75 years, the only income they have is social security benefits, are they required to file federal and south caroling state tax returns?

No, they are not required to file if their only income is from Social Security.

It depends on how much income they have, likely if that is their only income it will not be taxable or taxed very little, see below for the specific dollar amounts for federal. Also, generally, you are required to file a South Carolina Income Tax return if you are required to file a federal return

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