If your parents live in your household, you can include their income in your Affidavit of Support and execute I-864A. Otherwise, you file separate Affidavit of Support executed by them. You can submit signed copy of form 1040, all schedules, W-2, and letter from employer. Your parents will have to submit their 1040, if filed separately, proof of government benefits, letter that they will continue to recieve the benefits, proof of immigration status (birth certificate or U.S. passport or green card). IRS transcripts are not required but always better.