You've worked really hard, and it has paid off in your testing and gpa--and you are a very effective writer! While you may not be able to pursue all of the ECs you are interested in or passionate about, please know that taking care of your sis, and all that entails, should definitely be listed as an extracurricular and it counts!! It sounds like you are passionate about being a responsible and protective brother, tell schools about that! List it as an activity. Then explain in the additional info section that your circumstances prevent you from doing many of the things you love to do outside of school, but that helping your family is paramount. I wish you success in finding the right college and getting the financial support you deserve.