@Lilacmonsteri don’t think that is a particularly unpopular opinion. I think many people feel this way.
However, a lot of them ( not all, but a lot) are people with skin in the game. Namely people who have kids and want their step grandparents to treat them the same as their biological grandparents.
whilst I do agree with you that deliberately excluding step children is awful, I don’t think that’s what’s happening here. The photographer was being rotated, as pp said. So she won’t have felt excluded. And I don’t think it’s unreasonable for the grandparents to want a pic of just their bio grandchildren.
I have heard of grandparents who don’t give gifts at Christmas etc which is just vile. I would make sure I had a gift for any child who happened to be present on a gift giving occasion (Christmas, Easter etc) whether they were family or not, so to exclude a stepchild in this way is deliberate and incredibly hurtful and not something I could accept.
However, in blending families, you do have to accept that there may always be a difference between biological and step grandchildren.
Some grandparents don’t make a distinction and I think that’s great and very welcoming of them.
However, for the ones who are somewhere in the middle - including the child, buying gifts, being kind etc….but also wanting a photo of just their biological grandkids, I think that’s ok too.