Paperwork questions

[immihelp]

Hi,
I am sponsoring my parents to visit U.S. on visitor visa. But have some queries as below;
1) “Letter of Invitation” should be on normal paper or needs to be on my company’s letterhead (since I am an employee of my company)
2) Do I need to make my Parents Affidavit letter here in U.S or it should be in India. If in India should the Affidavit be on some sort of Stamp Paper or just normal paper?

Thanks in Advance for all your help.

Regards,

[immihelp]

1. Normal paper.
2. In India. On stamp paper.