When you first enter lord Mortimer island you get a vision of Emily been shot by Louis mother but later in the game you learn Emily has a twin sister called Emma so my question is is it Emma shot by Louis mother
Yes, it seems so. They both disappeared at the same time. We can only hope, that there was a misfire or a blank shot, but I wouldn't bet on it. The fact that Sarah misses a hand is quite disturbing. Anyway, when Necronomicon is the McGuffin, the stakes are high.
Well to be honest we don't know if Louis's vision took place in the future or not. Something tells me that it took place in the future and that perhaps Louis has a chance to save Emma with Emily's help.