Imagine Bella taking that picture.
I thought that too, but then rejected it because Isabella doesn't quite fit into the age group of Viv, Miranda and Lynette.
I'm not sure about Lana because she doesn't fit into the age group either. But Lynette seems to have some connection to the Royces and the photo is a Polaroid picture and we know that's because Jill has this Polaroid camera. Now, I don't know if this was mentioned or not, but Jill may have inherited this Polaroid camera from her sister Lana.
We should also consider Amelia because she could be around the same age as Viv, Miranda and Lynette. Furthermore, this unknown woman, Priscilla, could also be the photographer.
Either way, 3 people could connect the MC to his grandparents.