I don't know the official etiquette answer, but your suggestion seems sensible, and I think it gets the point across. I would assume both George and Martha are dead--if Martha was alive I think it should say "Martha Washington and the late George Washington."
Is there going to be anything like a tribute to deceased relatives--a song in the program or candles on the altar or something? That would also be a place to list them.
George and Martha Washington, parents of the bride
Louise Tucker, grandmother of the groom
etc.
I assume that, in addition to honoring the deceased parents, it's also meant to help avoid awkward questions like, "So where's the mother of the bride?" from more distant guests.
Speaking as a genealogist, it would be nice to have the women's original surnames listed.
John Adams and Abigail Benson Adams
The late George Washington and Martha Jones Washington
But, in the context of the wedding, that would only be useful if you had distant relatives attending who might be like, "Oh, this is Cousin Martha's daughter, right." If it's a small wedding, you probably don't have that broad an array of guests.