Harry's never going to anger the Grangers. Never. (He has a bit more leeway though considering he's practically a Granger now.)
The operation starts with some leaflets.
Leaflets about the signs of child abuse are sent to every house at Privet Drive apart from number 4. If that wasn't enough to get the neighbours chattering, the fact that Arabella Figg glares at the Dursleys every time they walk past would be.
Arabella Figg often babysits children around the neighbourhood, particularly a small (too small), thin (too thin) Harry Potter.
They are suddenly wondering their ungrateful nephew is. Apparently, he has gone to stay at a friend's house. Say whatever you like about the occupants of Privet Drive - they are certainly a nosy bunch.
They also stick together. Petunia is soon shunned from the tea parties and no one comes with Vernon to the pub. Dudley is treated with both caution and care.
When the police are seen outside their house, the entire street watches. Some are close enough to make out what is going on.
Petunia has a mental breakdown as she is arrested in plain sight for child abuse whereas Vernon becomes aggressive and attempts to harm the policewoman leading him away. He doesn't get anywhere close. Dudley is taken into his own police car. He is accused of being an accomplice though given his age and upbringing, leniency is sure.
The Grangers and Harry watch the scene impassively. Harry takes some twisted satisfaction at seeing their suffering. Only a little. Hermione has enough for both of them and soon she is cackling hysterically, the sound disguised by the various others in the neighbourhood. Harry has to hand it to them - the Grangers are good at revenge.
Hermione has to get it from somewhere, he muses, even as the Grangers talk to the authorities and he answers the questions they ask him as impassively as possible. Hermione sits with him the whole time, at his request it was allowed and she would have found a way anyway.
He isn't sure what the proper procedures are but the process is not helped by the appearance of some Ministry workers - Obliviators, apparently.
It ends with Harry staying with the Grangers, if they're willing to take guardianship of him. He tries to protest, really he does but all three of them are adamant so that's that.