Its a coming of age story about the MC, and the trials and tribulations that make him into the man he will eventually become (varying slightly based on the minor choices offered to you)
Bianca says she knows Jill through her father and became friends through riding her horses, Jill corrects her and says they were her Mother's horses and Bianca says "Fine, they were Amelia's horses".
The friends in the photo are called Vivian and Miranda. Unless Jill's mother changed her name no way any of them are her mother.
That said, doesn't stop one of them being family. Just not Jill's mother. Alternatively... one of the girls does look a lot like Bianca and DPC did make her his display picture.
Perhaps the connection to Lynette is Bianca. Biancas's family know the Royces and MC's family hence the photo of Lynette infront of what is now (or always was) the Royce house.
EDIT: Yeah, between Bianca being DPC's new display picture leading me to believe she will play a significant role in the story outside of just a random Jill friend and her resemblance to Miranda my money is on Miranda being Bianca's mother and she is the link between the Royce's and MC's family.
This also cleans up my previous concerns about the MC learning more about his family via Jill if you were caught by Jill sleeping with Bella. If Bianca is the link to Lynette via her mother it wont require MC still spending time with Jill discussing his family.