If you want help, you have to provide more information. For starters, full name (first and last) of your grandparents. Where did your grandfather get born? Year of birth? Where did they settle in the US? What year and where did they get married?
Ellisisland.org index only goes to about 1924 or so and certainly not for entries after WW II.
Another way to approach this is to ask about naturalization applications, papers, etc. If you can find the applications, it will tell you information about where they were born and how and when they entered the US. Were they naturalized? If yes email the nearest National Archives branch to where they lived and ask if they can find the naturalization applications. There will be a small fee if they can find the papers and photocopy for you, no fee if they can't.