itch.io

Yes, all of those things you mentioned have probably something to do with the lore of this game. I'm pretty sure that the teachers don't even want to do that, and that Albert meant that we aren't just the last hope for the lost souls of countless children, we are also the last hope for all the staff members. Maybe the sirens are a sign for a war that's going to break out between enraged ghost children and teacher demons? Or maybe this school is in an area where a war broke out and that's why no one cares about what's happening in this school, because everybody has bigger problems right now? (Those are just wild theories of mine.)

Edit: Other lost souls could probably be in Puppet and Doggos, and maybe even in Phonty. I got FNAF flashbacks right there...