[Haunted]

Hello.
I am in serious need of advice at the moment.
Before Christmas, my little sister (13) was hospitalised and after she'd spent a few weeks in the hospital, at the beginningof January she was diagnosed with leukaemia. Obviously, everyone in our family is really worried, and I feel extremely helpless in this situation, because she's always suffering (or at least most of the time) and I can't really do anything except reassure her that it's going to be ok (it seems like she's responding well to therapy, despite the various lows she's been going through), I can't take her pain away.
The advice I need, though, is mostly for myself (even though I'm open to suggestions regarding what to do to feel less helpless).
I'm sure some of you have seen me posting stuff about my father just generally being a piece of trash, and once again he is making my life a living hell. Since my sister was hospitalised, he's been extremely stressed and his reactions extremely unpredictable. When I'm alone with him, which happens pretty often, he sometimes behaves badly: the smallest thing can make him angry, he raises his voice very often and for the smallest things; I was already scared of him before all of this happened, but it's become so much worse lately. He's gone from "piece of trash" to verbal abuse, and the only reason why he's only been emotionally abusive towards me a couple times is because I'm trying my best not to speak to him (as in: I don't correct him when he's wrong, I don't speak about my problems/achievements, I don't disagree with him, I don't ask him to help me with the housework, I try to be as nice as possible even when he raises his voice, etc). My mother is rarely home, because she has to go to the hospital with my sister for treatments and various other things (like nausea, fever and the like) nearly every day.
I suffer from anxiety, my father doesn't take my disorder seriously; whenever my sister feels sick, I have an anxiety attack and stop speaking (I literally just shut up unless someone says something to me, and even then I tend to talk as little as possible) because my father gets twice as stressed and his behaviour gets twice as unpredicatable.
Being stressed myself, I find myself getting angry really often and for the smallest things too, but I keep it inside to avoid a negative reaction from my father. But I don't know how long I'll be able to keep this going. I do have a couple friends, but they're busy as well and I don't want to bother them for things such as 'my father left a candy wrapping on the table and I want to beat the shit out of him' - because that's how I react at first. It seems pretty obvious that I won't be able to see a counsellor for a while. I have no idea how to deal with everything, considering that I can't bring this up to my father without causing an exaggerate reaction, which could result in him yelling abusive things at me. I feel totally helpless, I'm scared I'll lose it and go back to being the monster I used to be when I had depression (and to self-harm, because I'm still addicted, despite the fact that I ddn't do it for two years before relapsing a few weeks ago - it's the first thing that comes to my mind when I feel overwhelmed). I don't know how to handle my fear and my anger anymore.