It must be a joke
Our story starts in Vernon and Petunia's house. They have just received a letter from their grown-up son Dudley.
Vernon asked, "Well, what does it say, dear?"
Petunia's mouth opened and shut like a goldfish, but no audible noise or words came out.
Vernon gruffly snorted. "Petunia, what's wrong?"
Petunia shakily handed him the letter without uttering a word.
Vernon glanced at it and read aloud, "Harry wants us to be godparents for all of his children." He smirked. "It must be a joke, darling."
Petunia adamantly shook her head.
Vernon muttered, "Petunia, dear, use your words."
Petunia quietly said, "It's not a joke. Dudders assured us of it in the letter."
Vernon inquired, "Why on Earth would Harry want to make us the godparents of all three of his children?"
Petunia shrugged. "He wants to forgive and forget, remember? Maybe this is him extending the olive branch, as it were."
Vernon sighed. "Hmph, I suppose. What harm can it do to pay them all a visit sometime then. We ought to at least meet these children of his, eh?"
Petunia nodded. "Yes, I suppose so."