Almost 5 year old granddaughter

I think your ex is unrealistic. She knows. And those bonds, however he resents them, should be let to develop as long as its safe. This child will resent him in the future. He needs to act in the best interest of the child.

I would just be honest and tell her the truth in a very gentle unjudgemental way, she can understand. You'll be surprised at how well children perceive things. She probably already realises that her life may be different than her friends. They do have little chats between each other, "is that your mummy and daddy", particularly if one parent is much older, ie. the grandfather. Just be kind and answer her questions in a thoughtful way, and she will be okay. Much live xx

Maybe time to review the day to day care arrangements. Having worked in social care this sort of arrangement is hard on children as they may feel they have no home base. Even more of a problem when she starts school. What she calls her carers is part of her identity and very important to her future wellbeing. Is there a social worker who could help?

Poor child☹️

I've been in the early childhood sector for years.
In that time I have cared for children of lesbian mothers and they generally call them mummy and mumma or mamma and mummy...insert the name of the non biological parent.
Their friends at kindy tend not to think too much about this, they just accept the situation. However as your grandchild gets older there others will question the arrangement.
It is important that your granddaughter is able to express her confusion but eventually she will have to decide on the names she attributes to her carers.
The idea of a photo book is excellent, kids at this age are visual learners and she may even swap the photos/titles around for some time until she is settles on something definitive. Good luck, it is a difficult situation but hopefully with patience and understanding things will sort themselves out.

This poor child is in an impossible family. I am sorry to say that, but no adults come out well. It's a disgrace this was allowed.

Welcome, glad you reached out. At age 5, kids can be deeply affected by family dynamics. Keep things simple, honest, and age-appropriate when talking to her. Stability and consistency are key. If there’s confusion around parental roles, it might help to gently clarify without overwhelming her. If possible, consider speaking with a child therapist, they’re great at helping kids make sense of complex situations in a healthy way. You're not alone in this.