Hey hon.....that sounds like a real rough spell coming up for you. In times like this I find it is best to journal. It sounds hokey at first, but nothing is better than to pour your fear into a page only to look at it with relief a week later because it no longer seems so scary. I try to rant out everything that has my juju all in a knot, then I highlight each seperate 'thing'. For each thing, I put it on one of 2 lists 1)I can do something about this 2)I can't do anything about this. The stuff that is on list 2 you must put away as something beyond your control. You can't beat yourself up over, worry about, second guess, feel guilt over stuff that is simply not in your control. Make up your mind to just shove those things out to see on a pile of sticks and set them a flame. Then address the list of things you can do something about. Prioritize it. Come up with steps to bring about the desired outcomes. Don't do anything fast though....what feels like your world falling apart usually feels less desperate in a few days. I don't know how old you are but I was 15 when my dad left....and the only thing I can think there is that is TOTALLY THEIR DEAL....has nothing to do with you or your siblings....and it sounds like any benefit of being a untied front for you and your siblings is being squashed by any unhealthy environment that marital problems create. How old are you?
Just don't try to ignore what you feel, yet don't let it overwelm you. I find jounrnaling helps because you are paying attention to your feelings of mourning and hurt in a very concerete way....and you can put the book down when your down. Take a deep breathe, shut the page, and say, 'Okay....all my troubles are there...I'm shutting the page on them for now but I'll return then them and they'll seem fresher when I do.' And allow yourself breaks of feeling purely depressed in between all this mess your going through. And vent away at places like here, or where ever feel comfortable to you. Willing to hear problems and give my take on them.