Funny thing is, when I put up the prompt "Sirius' prank" I didn't even think about this prank - and when I see this now I think, of course that's a natural place to go :)
I really like the idea of having multiple people telling their version of what happened back then. I've read fics from many POVs about this (well, mostly Sirius and Remus tbh), but not in the same series like this.
I do see Sirius as someone who could lose his head completely, and also as someone who had a lot of love for his friends and deep down also for his brother. I really like how you've let both of these sides show here. Oh, and how good that he decides to tell Harry himself what happened, and how he opens himself up by encouraging others to tell him their side of it. That couldn't have been easy for him, and shows how much Harry matters to him.
Great start to this series!