Yeah, I agree.
I understand that you don't want to do it all all, but you should tell her that you don't mind watching her kids on certian conditions....
1) You be paid to watch her kids
2) Paid additionally or inclusive of additional work/chores (dishes, cleaning, etc).
BUT, First of all....you aren't being paid. Next topic is the family responsibilty. Yes, you are her sister, but you would still like to be treated NICELY for doing her a FAVOR in watching her kids without being compensated. Another thing, you are getting behind in school, and that's not a good thing at all. I don't care if you go to public, private, or online. Getting behind on your education is not a good sign.
Tell her that you are making sacrafices (your friends, your time, your life, your school, your car, etc.) and doing this out of the goodness of your heart and the fact that she's family and you don't want to see your nephew and niece be corrupted by some wierd babysitter.
It would be nice of her to TURN the cable (internet AND tv
) back on and for you to be paid for you to continue any longer in this demanding job. Unless you have any other compromises you want in leiu of being paid.
I hope it gets better for ya!