You keep making vague references to a merit grant at Auburn. What’s the actual net cost to your family for each school? It looks like Auburn’s highest merit award is $15k/year. The next highest one is $8k. That brings the net cost to $34-41k/year. Can your parents afford an additional $40-68k for your education?
Where your sister plans to go to college doesn’t matter. If she’s thinking about less expensive schools it doesn’t mean you’ll have more to spend.