Finacial aid...help pls!!!!!!!!!!?

im 18 yrs old...and im trying to apply for finacial aid!...but their asking me for my parents 05-06 taxes or prove of income...heres my problem!....my mom only has taxes from 1999-2000....my dad was in prison for 5 yrs...and my mom was a house wife and was renting rooms for a living and was even recieving food stamps....so obviously we dont have a lot of money....and my parents now live in rosarito..baja calif!...and i live w/ my older sis....so i figured maybe they could use her taxes...but they want some sort of doent that say shes my guardian...and im really confused...how would i prove my parents taxes if they didnt have any...would i qualify for finacila help....pls....help???????