Having your sister and you in college at the same time would increase your financial need but would have not any effect on merit scholarship possibilities. You need to look at the California private schools where you have a better chance for merit aid based on your SAT and GPA. Some schools to consider are Stanford, Occidental, Claremont Colleges (Harvey Mudd, Pitzer, Claremont McKenna, Pomona and Scripps (if female), University of San Diego (not UCSD), University of San Francisco, Santa Clara.