Ok, in the interest of damage limitation, by which I mean your mental/emotional state rather than your weight
whilst you are at your mum's (you could practice this week before you go)...could you first of all take charge of preparing breakfast each day? It's been proven that if people eat white carbs/sugar for breakfast then people crave more of the same all day-as cereal fulfils this definition perfectly choose a delicious and protein rich alternative. Smoked salmon and scrambled eggs with some wholegrain toast, Greek yoghurt with raw nuts and berries/banana, peanut butter and banana on wholegrain toast, buckwheat pancakes with fruit and full fat yoghurt, asparagus and dippy boiled eggs, bacon, mushrooms and baked beans, spinach and poached eggs on wholegrain toast....
Plan - yes plan - a 'binge' for each day. It sounds as if you are very aware that bingeing is inevitable so choose it and have it on standby for when you really feel you need it. By giving yourself permission to eat 'bad' food, to use it as you need to (because a binge does serve you in some way, it is a coping mechanism) you take away a lot of the food's 'power' - does that make any sense? So when you feel the impulse to eat, try and stop and think whether what you are feeling is hunger (in which case could you choose to eat something more nutritious than sugary carbs) or stress/something else (in which case could you take a walk, go for a run, rant on here, have a bath, paint your nails?) If you are at that place where you need the biscuits (or whatever) then have them, but try and slow right down, breathe, taste and enjoy them.
With all this, keep in mind that your coping mechanism of bingeing could be much worse-drugs, alcohol, gambling for instance do much more harm than food. And you, as you recognise, are in a place where you can relearn (though it will take time, practice and patience with yourself) better ways of coping and being in relationship with food and your body. Your sister isn't so lucky
, she's much further along that road of control, I hope she gets better soon 
Wrt your knee, I sympathise, I love exercise and being injured is so frustrating. Is there a yoga class near you that you could try?