EEA2 extended family member

Good afternoon , I am looking for information about applying for EEA2 extended family member residence . My sister living in london to 7 years , and she married with a Portuguese .
Last year I was in London for 6 months studying and also made ​​a donation of eggs for my sister , now 8 months pregnant .
I wonder if we could ask the family visa even though I am of legal age ?
I got in london on 15/05/2013 with my mother to the letter of the course with duration of 6 months and the letter from my sister taking responsibility for us . She paid my course worth 2300 pounds . Additionally , she helped me pay the tickets . I was at her house with my mother . returned to Brazil in November and I am unemployed since March 2013.
We would like to ask claiming I 'm dependent on it ?
It helps me monthly depositing money into my account?
The fact that I'm still unemployed and being single help?

Also, my mother is 76 years old and can not be alone , which makes me work . If I can go to London, my sister and I can work at different times and so my mother would sempore someone to stay with her .
My mother is retired and helps me at home, but the money is not enough for all expenses .

thank you