As grandparents, you have a valuable asset, your wisdom. I learned SO much from my grandfather. The things that I have learned carried me through to this day. He was a first generation immigrant from Finland, grew up poor, worked the land, built roads and logged in the upper peninsula of Michigan, joined the military and was part of the Pacific fleet engineering crews building airbases on the various islands during WW2, and later became a machinist for Meuller Brass in Port Huron, Michigan. He raised 7 children in a small country home. He taught me A LOT about growing food, storing food, growing houseplants (one of my life-long special interests), using farm equipment, using natural ways of controlling garden pests (ladybugs and chickens), composting, woodworking, using a metal lathe, and how to do home repair and maintenance. He always kept himself busy with some sort of project, and he loved sharing what he was doing with me. He lived until he was 90. Passed away several years ago, but he is one of the few people in my life I think of often, even now. I miss him dearly.
The reason I am saying this, is that the word "autism" in Greek, means "self" or "auto", and explains our social experience. We all struggle with connecting with people and maintaining relationships. There is a long list of brain anatomy and physiology and neurochemistry involved that account for this. It's certainly not for a lack of "trying". Most of us would rather talk about "things" and "ideas" than people. So, I certainly appreciate your efforts with trying to have your grandson connect socially with others his age. It is a valuable learning experience, but, if you sense he is failing, please understand that it is part of the autism experience, as frustrating and painful as it may be. Young autistics really, really struggle with this and it's difficult to deal with, and for everyone to witness. Your role as grandparents will be valuable as instructors and mentors. He's going to need life skills whether it be recognizing and dealing with people who might take advantage of him, or actual skills he can use in his daily life and potential work career.
It is good for your grandson and you all to understand that he is not a "failing neurotypical" but rather a "normal autistic individual". Having said that, it may take decades before he can settle into the idea and accept his situation. Now, if he happens to be lucky and connect with a wonderful life partner, both need to understand the challenges of the autistic mind when it comes to the importance of communication, perspective taking, and context. Many couples will struggle with this.
At any rate, welcome to the forums.