My son-in-law and his wife are John and Kate, which sounds like “Jon and Kate” although I guess those two aren’t fictional (I’ve already forgotten why they were supposed to be famous).
And I knew a Tom and Gerri for a while.
My aunt is the Jill in a Jack and Jill.
We had family friends named Bob and Carol.
I knew someone named David Brinkley, who married a girl named Christy. Not exactly a well-known pair, but it always amused me to think of the two famous people I knew, David Brinkley and Christy Brinkley.
I had neighbours named Ken and Barbara. Inevitably, they were known as Barbie and Ken.
Gary Trudeau and Jane Pauley’s twins are a pre-Friends Ross and Rachel.
During the Beatles heydey, I knew a Paul and Jane.
According to tradition, the parents of Our Lady are St Anne and St Joachim. They’re the patrons saints of the small Spanish town where I grew up. While the people themselves existed, the names aren’t necessarily true, which is why I’m counting them as fictional.
I do know an Ana and Joaquín from that town; she says that for the longest time they didn’t want to date each other because the jokes just wrote themselves, but they eventually had to admit that they liked each other too much not to. They may be the only couple in town who managed to avoid calling any of their daughters Mary-anything, despite having four of them (and two boys); they also asked their daughters to please, please, please not give them any grandson called Jesús.
I know a couple called Mxyzptlk and Gsptlsnz, but they are very odd.
My inlaws were Dick and Jane.
Not a “couple” per the OP, but my sister and I are Peter and Wendy. We managed to get past college before someone noticed it and pointed it out.
Me & Mrs. are Tim & Jill. Our dog was Taylor.
I’m a tool guy with too many wounds and stitches.
We had a neighbor, Mr. Wilson, but we could see him.