How can i keep my family problems separate from my school problems?

its a lot more complicated than wht chya think. ya see. my mom went out of the country and left my older sis and me livin in in da apt., but then my older sis did A LOT of over spending. so in the wun month that my mom was away she spent over $1,200!!! and we're poor and money doesnt come easily. so0o0. and yeaa id admit to spendin a little with her. but she just went out of control. well now that my mom is back we are much better, but still have that huge debt. and now im workin a part-time job, and doin all i can do to help, but then i have school to balance too. how do i deal with my family crisis WITHOUT it affectin my grades?? k/thanks