You also need to keep in mind that for your first year you will be the only college student in your family. It is the last 3 years you’ll benefit from two in. Be aware that your college will ask for verification of your sister’s enrollment plus how much she’s paying when the time comes.
The advice from erin’s dad re: find schools where you are in top 25% score wise is good. You haven’t indicated possible major but perhaps Dickinson or Lafayette. Both can be very generous. There are schools with full tuition packages. University or Richmond for example where you don’t apply but could be selected based on stats. Wasington & Lee and Tulane require seperate apps. All of these deadlines are early. Like december 1st.
We had twins so this was factored in from the get-go. But you might want to ask FA folks at schools you are serious about how having 2 in your sophomore year might impact aid. Also make sure you are aware of any GPA requirements to keep merit $$ in subsequent years.
Good luck. You sound like an excellent candidate and should have options come next spring.