How should I give my uncles a reality check?

I have 2 uncles one is 24 and the other is a senior in highschool and hes 18. My grandparents work their asses off to support them and they don't want to make the effort to get jobs and help them out. The older uncle can't keep a job because he gives up very quickly and complains all the time that his back hurts when he works or if he gets hurt at work, he makes it seem like he can't work again. The younger uncle has stolen over $2,500 from my grandparents and has spent it on video games and pizza, on 2 separate occasions. He has no respect for my grandparents and ignores them and when im not around he cusses at them. They both lock themselves in their rooms and spend days on their electronics playing games and only come out to eat or bathroom. My grandparents give them so much leniency. My grandparents marriage fell apart because when my grandma gets on the boys my grandpa backs them up. When my grandpa gets upset he yells and walks away so he doesn't have to deal with the problem. I want my grandpa and grandpa to be able to enjoy their retirement in the future instead or supporting my uncles til they both pass. How can I give them a reality check? My grandparents aren't going to be here forever and no ones going to take their place to support them. My grandparents are tired of it and I want to figure out a way to help them.