回复：关于父母签证的问题

they're not necessary. but for the safe side, it's better to provide them. they're not difficult to get. ask your company HR or your boss to write a letter to verify your employment. you can download the i-134 from USCIS website, fill it out and have it notorized by your bank or your company (if there is a notary public available, and usually it is a free service).