Advice on invitation scenario for a first birthday

Ok, I'm going to try to make this clear as I know the scenario is very confusing. I am friends with a former coworker that has a granddaughter who is 3. She kind of adopted my sons as her grandsons and treats them very well. I would like to invite this friend and her husband to our DS first birthday party. Since it's a first birthday party, and will have entertainment for little ones, I would also kind of like to invite her granddaughter. She watches her a few days a week and we always say we are going to make a play date together. I do not know her daughter, (the mother of the granddaughter) but I am friends with, and will invite her other daughter.
If you got this far, thanks for reading!
So now, do I invite the granddaughter? If you think I should, how do I word the invite? Do I have to invite the parents of the granddaughter as well?
Any input is appreciated!!!

Re: Advice on invitation scenario for a first birthday

I would send an invite addressed to your friend and then verbally say to her you are welcome to bring granddaughter if you want.

Re: Advice on invitation scenario for a first birthday

I would address it to your friend (the grandparent) and a little handwritten note inside. I would say something like, "we would love if you brought___ to the party!"

Re: Advice on invitation scenario for a first birthday

Re: Advice on invitation scenario for a first birthday

Thanks for the advice! It makes sense!