M.S.
I would probably go, and I would probably tell my mom that I was going to go. I wanted to share my own "helping to fix a family relationship" story. I've learned a lesson about people's relationships, that they are more complicated than we know, as outsiders, and also that we should stay out of other peoples problems and disputes, except to be there to listen.
I strong-armed my husband into contacting his mom and inviting her over for mother's day, 3 years ago. He hadn't spoken to her in 7 years. I didn't understand why someone would be holding this "grudge" and thought it was awful that he wasn't making an effort with his mom. We all live in the same area (within 20 minutes). It went fine, meeting her, having her for dinner, sharing our new house with her. They even talk on the phone sometimes. But I forced this on him.
Now that we have our own kids, I understand why my husband was hesitant about having his mother in our lives. I don't want to say mean things because I honestly believe she did the best she could as a teen mom in her situation, but she's not the grandmother I expected or hoped for. She never sees the kids. She refuses to babysit. She doesn't help us at all. And we're resentful of it. My mom does more and sees the kids more, and she lives 800 miles away. Would we be in this situation if I hadn't gotten involved in other peoples' relationships? Probably not. I've helped to open wounds that I didn't know were there, which have made my husband sad and even more resentful of his mother.
So I would go, and develop your own relationship with your uncle if you want to, but I would stay out of trouble trying to fix what's wrong between him and your mom - that stuff is truly between them and no matter what you do, you can't fix it.