I think you need to work out what this will look like.
The best thing for your daughter is a gradual introduction, and only over time will grandparents etc get involved.
So you could start with books about different kinds of families, so she's comfortable with that idea before introducing someone new. Tell her how you met DP, that you knew her before you knew him. It's really important that she understands that first. Think about adoption stories, how children learn about that.
Then photos and letters from her birth father.
Then meeting in person.
Then spending time with him, without you.
Then his extended family.
That's all going to take time, so you'll have time to get used to it.
Your DP still gets to be who he is- the man who raised her, 'dad' if that's his name. Her biological father can be 'mummy's old friend, who is your birth father, because mummy didn't know dad then'.
This is all about what's best for her. He effectively gave her up, he needs to understand that contact needs to be gradual.
It may help if you can reassure him you know it's good for her to know her birth father, but you want to do it right.