First of all, the Death Eaters had implicit orders that Harry was Voldemort's to kill; they had been specifically ordered not to kill Harry.
This is incredibly nitpicky, but it says that the two killing curses missed Harry's head and they clearly did not hit Hagrid. Harry sent stunning spells, but it does not implicitly say he sent stunning spells to block Avada Kedavra spells. It just says he sent stunning spells. As for red meeting green and colliding in a shower of sparks like fireworks, I want to say that Avada Kedavra is not the only spell that is green. Canon says that Avada Kedavra is not blockable (except by Harry's head), so I err on the side that the green lights were other spells. Here's an example of another spell that produces green light that is not Avada Kedavra:
Ron plunged his hand into his robes, pulled out his wand, yelling, ‘You’ll pay for that one, Malfoy!’ and pointed it furiously under Flint’s arm at Malfoy’s face.
A loud bang echoed around the stadium and a jet of green light shot out of the wrong end of Ron’s wand, hitting him in the stomach and sending him reeling backwards onto the grass.
Chamber of Secrets - page 87 - Bloomsbury - Chapter 7, Mudbloods and Murmurs
ETA: Per DVK's suggestion, I'm including my comment made a few hours ago in response to a comment by Pureferret:
I think it has to be a spell other than Avada Kedavra, otherwise it would not be blockable. Snape was a Death Eater and he used Sectumsempra, not Avada Kedavra, during the The Seven Potters scene. A lot of tactics are used during war. Above, I gave a canon example that is green, but is not Avada Kedavra. I'm sure there are other spells in Potterverse that are green, but have been left unspecified by J.K. Rowling.