did they ever show them?

Elaine's father appeared in the episode Jerry has the reversable jacket. Her mother is never shown.

It is just said that the mother lives in Maryland, but she is never seen.

The dad is a big meanie!

did they ever show them?

Elaine's dad was in one episode, if I remember the name of the actor who played him was Lawrence Tierney. But the cast later said he seriously scared all of them and that's why he was never on Seinfeld again. It's interesting that you're a Star Trek fan. Because the actor was also in 2 Star Trek episodes on different Trek series. He was first in an episode of Star Trek: The Next Generation, in The Big Goodbye I think it was. He played a holodeck character (gangster type) named Cyrus Redblock. Then he appeared on an episode of Star Trek: Deep Space 9 (I can't think of the name of the episode right now). His character wasn't given a name, he was simply called the Regent of Palamar. Palamar being an alien planet, he was the planet's ruler.

Ed.