Considering neither Greg nor Ray had any family so to speak, here, they had been very liberal with calling their various friends 'uncle' or 'aunt', wanting the girls to feel like they had a large family. Wanting them to feel loved. Greg was more conservative with it than Ray, but he'd been the one to first change Jack from 'Mr.' to 'uncle', without thinking about it. He didn't know what Jack had, that kept him interested, but it was there, and he wanted the man to be a part of his daughter's life. Maybe he just wasn't used to the idea of friendship. One way or the other.
The girls were more than happy to show Jack how things were done, poking and prodding at the small screen on his lap between them, oblivious to the man himself.