I made a really good summary in my thread about this. As long as you pay attention and follow the different hair it's quite easy to follow, but you can't get distracted, I couldn't even play on my phone at the same time like I normally do. 
I think it's Sophie, not Alice. I think Alice died, possibly Sophie had a hand in it and she wanted her life. They would have been taken around the same time, they were the same age and from the photos of Sophie in the papers, they looked quite similar, especially the eyes. They made a point twice of saying how Alice tattooed herself so she could have done one on Sophie too.
I reckon either the fake Alice died not long after returning, or they go to find where they were held and find the body and that is the real Alice, hence the grave. Possibly. Or the Alice that returned died in a fire and the father and brother feel guilty because they couldn't save her.
I think only the mum suspects she isn't Alice. Baptiste said at the end the girl who returned wasn't Alice. At first I thought he meant because she would never be free and always trapped in her mind but I don't think that's the case now. Unless it's a double bluff to make us think that. Possible.
The brother has also promised something to Alice.
Not sure what the photos are about. Something the mum doesn't want her family to know about so just be something to do with her and Baptiste not believing it was Alice.