Yes, it makes way more sense than what you originally posted. If you had posted all those details before, it would have been understandable why it's not that easy to just walk on over there. I am sure out of your frustration that you just didn't put that in but please remember that we don't know you or your living situation.
We only know that you put a question for help and we can only help based on what information you supply us with.
So yes, this makes a more complete story for your issue and now that you put all that, I believe the advice will be a bit different.
Having said that, I am a pro at long distance family relationships. I live a continent and ocean away from my family and I opted not to argue at international rates because there is always some issue that comes up and my mother will call me to complain as if I could just walk over and help.
I am not even in the country where they are and I am coming between family members, lol go figure. With that, I have just ignored these "moments" and acted as if I am not bothered by it. I have a journal and I post my biggest secrets in there...and that's that.
If you are really frustrated, write a letter to your parents expressing how you feel and when you are finished, throw it away. It helps ALOT.
It still seems however that your sisters situation is pre-occupying them as this also involves one of their grandchildren. So I stick by what I said before regarding the book for them.
You could buy one of those photo albums that has a space to write a caption. And take tons of pictures of your son doing whatever you think your parents would love to hear about or doing whatever it is you would call them for to tell them about what your baby did.
Keep a journal of what he does and when he does it. Documenting this is good all the way around for you and them and him when he is older.
At the end of each month, and I am hopeful you talk to them before hand but at the end of each month or even every two weeks. Send them this little pictoral update. They will appreciate it.
Try to call them once a week and even if it is just for that one minute, so be it. Or if you can not handle this, then write them a letter and send some pictures of your baby doing what he does best...being cute. 
You don't need to spend a lot of money to do the picture thing but I would think, as time pressed as they seem, an email will go unanswered. If you send them a small little letter with a few pictures and info on the back of the pictures, it will get their attention more than an e-mail or phone call.
I really do feel for you in your situation and I am glad that you cleared it up regarding the "whole picture". Not that we need to know every little secret. But when you ask for help just remember, we can only give you advice based on what you ask/put in a post. take care and best of luck and if you need an ear...feel free to email me.
xoxo
aaliyah