I would say try to keep an open mind with respect to Choate and Lawrenceville, and ask them to do the same with respect to Hotchkiss and St. Pauls. No decisions have been made yet. Wait and see where the acceptances come in, then do the revisit days. If, after the revisit days, you are still not on the same page, try to craft a well-reasoned argument for why you should choose school x. Think through how you can make it work for the family.
Speaking from the parent’s perspective, it is a sacrifice to send a child to boarding school to begin with. And your parents are trying to make it work for your family. Presentation makes a big difference in how I respond to my DDs’ requests. If I get a whiny, poor-me attitude, or an aggressive entitled attitude, I tend to dig my feet in. If instead, I hear a well-reasoned, calm request, I tend to give it more consideration.
Good luck to you and your sister.