It is a very risky idea to borrow $80,000 (for 2 years). Do you have any idea of what the repayment will be? (You'd need your parents to co-sign and I hope they wisely refuse to burden you with such a debt.)
The monthly payment on an $80k debt will be at $920 a month for TEN LONG YEARS.
Do you have any idea of what such a debt would do to your life between the ages of 23 and 33? That would be like paying for 3 extra car payments (in addition to your own) for 10 years. While your peers would be moving on with their lives (buying homes, etc), you'd be stuck with these burdensome loans.
Do the FAFSA and CSS (if school requires) to figure out what your parents can pay. Your sister will do the same. The fact that you'll have two in school at the same time will be considered.
But, with such a high income, your parents should be able to help pay for BOTH of you. SERIOUSLY!!!!
I hope your parents will not agree to such loans for you. If they want to borrow and repay, that's different; they make a lot of money. But a newly-minted graduate doesn't make that kind of money.
Lastly, if you can't afford a private school, then you need to go to a good in-state public. What are you majoring in? I seriously doubt that your career plans require that you go to a pricey private.
I know that my words are not what you've wanted to hear. But, believe me, I'm a mom who truly cares about kids. When I hear of such plans that I know will wreak havoc on your future life, I have to speak up.
Good luck.. Get your degree as cheaply as you can. Then go have a wonderful life.