For SAT IIs -- take writing instead of lit (that's the test they want)
It is very important to have AT LEAST 3 years of the same foreign language. I am not sure why you are not taking that Spanish. If it is because you hate it, you may want to rethink it. If it is because it's too easy and a waste of your time, take SAT II and get >700, then you are probably fine. (There is no way your brother's status will replace a year of foreign language.)
I would not worry too much about "official" leadership positions. It sounds like you put a lot of thought, time, and energy into tutoring. Make sure to let them know that through your essays. Everybody is a president of some club, and no one cares about it, unless they actually have something accomplished.
And don't worry about the girl. There is no quotas for schools, and if she will be a recruited athlete, she is in a different category all together. Plus, there is nothing you can do about it...