I'm so sorry to hear about the loss of your Grandpa - and I wanted to say that I know what it's like to be far from home when something like this happens.
Last Februrary, one of my Grandmas passed away, and there was just no way I could get to the funeral. In the meantime, I also experienced a level of sadness that seemed huge and overwhelming, even though my Grandma had been dealing with long-standing Alzheimers and/or dementia, and had been living in a long-term-care facility for about a decade.
It was supposedly 'expected', but it still hurt a whole lot.
The only advice I can give you is that it might be really worth your while to write a poem or a story to be read at your Grandpa's service.
I think it's important to be able to share memories with the rest of your family, and if you can't be there in person, then writing something - whether it's read at the memorial service/funeral, or just shared with close family members - this will go a long, long way to feeling connected and it also helps you find a way to explain to everyone else just how much your Grandpa meant to you.
Like I said, I couldn't be there when my Grandma passed away, but what I did is gather up all kinds of photographs on my computer, turned them into a slide show (just for myself), and I then found all of her favourite songs/music on You Tube - I listened to her favorite songs, looked at lots of photos and ended up writing something that was read at her funeral/memorial service. I got a phone call, mid-way through her service, and it was my Mom, saying that everyone loved what I wrote and that they had gotten to know my Grandma through my eyes, that everyone was crying and they thought that what I had written was beautiful.
I guess what I'm saying is that it's time to share with the rest of your family how much your Grandpa meant to you - and that by telling your own stories and sharing your memories, you are bringing him to life in a way that only you can do. It'll turn out that you have some memories and experiences about your Grandpa that no one else has, and I'm certain that the rest of your family would *love* to hear these things, even if you can't be there in person.
Sending some really big hugs.