Originally Posted by 2Face

I went for the same reasons (basically that my grandfather was aging and I hadn't met him for long time).

You are absolutely on point with this. All you need is the Doctor's letter on his official letterhead basically saying that your name and that you are his grandson and are advised to meet your grandfather, mentioning his name, and basically explaining what condition he is being treated for. Very short letter.

Along with that Doctor's letter, I would include a cover letter by you explaining and the birth certificate and picture should suffice. No need to notarize. It will be approved 100% if you fill the application accurately and submit these few items.

Good luck and hope the best for your grandfather.