Awful behaviour OP.
The most important person in this is your daughter.
So I would step well back and choose to relegate your parents.
Don't speak about them, don't mention them.
Talk to your daughter about other things.
By doing this and not giving them status, she will take from your lead.
It is awful for children to see this and terribly hurtful.
I haven't had it in my family but over the years a few friends have mentioned it a bit.
It is always the first set of grandchildren getting the priority attention.
One of my friends had this with her inlaws.
She found it very hurtful as her own parents were dead.
It was her inlaws daughters children that were the very clear favourites.
They did sleepovers and days out.
My friends children just weren't ever invited.
The boys were VERY aware of it, and it did hurt them.
They NEVER visited my friends home.
She mentioned it once and was dismissed as being silly so she let it go.
So she left it to her husband to visit his parents and only went infrequently.
Her sons grew less interested in going.
She liked her sister in law, but it obviously suited her that her children were given so much attention, particularly when they were young.
Her BIL got a promotion to the US with his company and they moved.
Huge tears and drama.
You know the rest of course.
Suddenly they were calls asking when were they coming to visit?
When could they see the grandsons?
Could they visit?
Her boys were mid teens by this stage and had zero interest.
She didn't intervene, she left it to her husband, as she didn't feel her boys should be suddenly expected to visit weekly when they didn't see them more than once every couple of months all their lives.
She kindly hosted them sometimes, but she never insisted her boys be around as by this time they had lots of matches etc. and their own lives.
Her MIL is dead now and her son's never visit the grandfather, they have absolutely no interest.