Since your parents are the 'developer', they can probably depreciate the Mac you're using, and write off the $99/year fee.
Yes, Apple sends the full 70%. Yes, they want a SSN (or EIN) so they can tell the government (IRS) what they paid (your parents).
Are your parents technically sophisticated enough to deal with Apple, etc? Perhaps a better option would be to find a kind soul who is already an Apple registered developer who can publish your app, and pay you a (high) percentage of the proceeds.