Thanks.  If sometimes the characters seem a little odd, please remember this is a VERY AU universe, where everything turned out differently than in the books.  In this reality, James, remus, & Sirius were never enemies with Severus in school, despite being from different Houses.  They were all friends with Lily and with Severus.  They all fought against Voldemort in their own way, Severus invented the potion which inhibited Voldy's magic, which allowed James, Sirius & Remus (Aurors) to kill him BEFORE he ever attacked Harry, so Harry was never the Boy Who Lived here, just a wizard child, albeit a very strong one.  James lost his life in the attempt however, which is how eventually Sev ends up marrying Lily and adopting Harry as his son.  (That is all detailed in WSG).

Severus main problem here is not the Dark Lord, but his awful childhood with Tobias, which is also explained in Never Again.  He was never a spy, never a Death eater, and so he is not the bitter and angry man he is in canon.  yes he is still sarcastic and he has a temper and is strict, but he is also much kinder and very wounded in spirit, though he tries to hide it.  His profession as a Potions Master Healer brings out a very caring side of him, and so does his adoption of Harry.  His friendship with Lupin, Sirius, and james has also helped him. they are a support network. 

As for Sirius being afraid of needles, well I've known guys who are soldiers and others who are very macho go all to pieces when faced with a shot.  Everyone has their Achilles heel, and I figured this could be Sirius's.  For Remus it's his werewolf curse, for Sev it's his temper and his childhood trauma.  James's was his obsession with killing Voldemort and being a hero.  They are all flawed and that's how I present them in this series. 

Hope I've cleared things up for you a little.