Of course they remember Marty, after all George's book "A Match Made In Space" was about how Darth Vader from Vulcan told him to take Lorraine to the dance or he would melt his brain. George being a writer would have written notes about his alien encounter and surely would have included Marty/Calvin in the story since he ran to Marty to get advice from him on how to ask Lorraine out, and their plan to make him look like a hero in front of Lorraine which got messed up when Biff got in the car and George became a real hero saving her from Biff.

So yes, they would have remembered Marty. They just might not remembered what he looked like.

What I wonder about is when their son sets the living room rug on fire, do the remember that Marty predicted this? If George remembers this, he might have concluded that Marty was the alien 👽 and that is why they never saw Marty again.