While the movie might focus on the Spengler family, perhaps we could meet new generations of Stantz, Venkman, or Zedmore as well.
It’s possible the new movie could introduce us to the children, or even the grandchildren, of several of the original characters.
Of course, there was no indication that Egon Spengler, or any of the Ghostbusters had kids, but it’s been 30 years since Ghostbusters 2, so it’s certainly possible they all settled down after the last movie.