i advise you to listen to Oddball and Cholly. i can tell you that moving out on your own when your earning a wage is hard enough so i would imagine moving without one would be extremely difficult.
i suggest you save, save, save and then consider moving. take control of your own finances and pay your share to your grandma yourself. that way you can save as little or as much as you want without anyone seeing or knowing. should they find out you have a little saved they may ask to "borrow" some. i can tell you that you will likely never see it again.
from the way it sounds, you are your aunts meal ticket because you pay a large amount of rent and food while also paying some of the bills, she pays very little. if you leave she will have to pay. your grandma will also have a stake in you staying. they will probably try and prevent it because you pay so much money in.
if your going to move you need to save. to save you need full and sole control over your finances so you can account for every transaction. if i remember correctly months ago you said that your grandma has control over your income and inheritence from your mother if that is still the case then that has to stop. if your grandma refuses to give up financial control then speak to the charity you are working with to get advise on your rights.
and for as hard as it may be, you need to stop buying fish and tanks. only buy essential supplies for now, ie filter media/meds/food. that will allow you to save even more.
good luck.