InGlorious
I don't know why people like Sirius Black so much or why there always has to be a forced relationship between Harry and Sirius even more so at this point where Harry already has someone who has supported him unconditionally for a long time at this point in history he is quite useless and it can be more of a hindrance than a help, It's probably a way of tying Harry to the magical Great Britain used by the author, I understand it but I still don't like Sirius probably because of his characterization in the fandom.
who's to say who will join harry side just go with the flow their are plenty of witches and wizards that will join him later on besides that war is mostly a game of thrones type battle unless the death eaters get fidgety and try something then harry will have the green light to wreck their entire house