Can't tell the difference.
Not fussed on either of them either.

To tell them apart, Amy is the one who almost always has a very smiley face and a more wide eyed friendly look about her. She is also a complete chatterbox and seems to talk more than Sally. Sally seems a little bit quieter and is the older one I think, she has a slightly more serious resting face.

Amy is the one who picked Aaron in the game of truth or dare and spent ages trying to apologise when he got upset.

Amy seemed to have an understanding face when Aaron nominated the twins, Sally less so.

Amy also had the discussion a few days ago with Eileen and Nick about the amount of horrible trolls who picked on her online, told her that her face was lopsided and called her "baggy fanny" etc and that she really let it get to her, and how her Dad was worried about her entering the house because of how much it affected her before but that this time she said she wasn't going to read any mean tweets etc when she leave.