The silver achievements are (according to my memory) defeat all enemies and find the extra characters with their respective scenes. The extra characters . . . . I mean, I just wandered around for the quests, and I recall that No. 3 can be found with her boyfriend in an extra-deep alleyway after you manage to meet the depressed dude (caus he removes obstacles and reveals more paths). No 4 is also with her boyfriend and in a room somewhere down east north, I think? I met No 4 pretty late in the game, so being patient and looking around the whole area is key. The gold achievement is to achieve all achievements. BTW No 2 is her sister, so you can expect the scene for the TRUE ending (i.e. you've messed around enough to be corrupt enough to screw your sister with a dildo)