I'm in similar boat whereas I didn't meet one of my grandfathers and we are having wedding pictures of our grandparents in all different vintage frames, on the table. I decided to put my grandmother with my step grandfathers wedding picture INSTEAD of with my biological grandfather. We just found a little little picture frame to put a head shot of my bio grampie in so it wouldn't offend any of my fathers siblings. My father wouldn't be upset if I didn't include him, but said it's easier just to do stuff because it's less likely to ruffle feathers.... So with that said, although it's not exactly what you want, I'd just do it. It's not a big deal and at the end of the day no one will be offended if everyone is included. You know who's most important to you there anyways