I'd say move out, around here you can get rent form around £50-60 ex. bills, so I'd talk to your sisters and see about finding a 3 bedroom rental accomidation and move in there, you'd all save some money, even after bills and food, etc.
Alternately, take the full student loan and move into halls, at least for one year, and then move in with classmates/housemates the year after.
I pay £50 a week to my parents all inclusive (bills, food, etc). But I also help out by doing the weekly shop, gardening, cleaning, etc. I want to move out as soon as I can, but being unable to find work as a graduate tends to stiffle that somewhat.