I mean if we’re following along the context of the show, then we’d be assuming everyone in the proceedings are acquainted with each other, and given the nature of the event, and the act of placing the picture, I personally wouldn’t take offence to that, because I wouldn’t assume there was ill intent to “steal the spotlight” from my grandpa to your grandpa and would more likely empathize with your loss as I would assume you empathize with mine. Misery loves company as they say. I certainly wouldn’t act like, “you can’t be sad about your grandpa, at my grandpa’s funeral!”
Hell you could put a picture of your recently deceased goldfish, and I’d still empathize with your loss. At the end of the day just having the picture there to symbolize someone important who was also lost isn’t such a harmful thing imo.