Nowadays, you can't rent with cash at most rental agencies, and only the renter can drive it, unless you want to pay extra.
   As long as the driver is 18, has a credit card to charge a large deposit onto, has active full-coverage auto insurance on his own car, rents a passenger van or large car or SUV, and is willing to pay the additional rental indemnity insurance that the rental company will offer, it shouldn't be a problem.  The others can kick in cash to reimburse to renter for all this plus gas, tolls, etc. 
  I would never loan or rent my vehicle out to anyone, even to family members, but that's just me.
  Let 'em get their own, just like i did.  It 's the only way to insure total responsibility, and no bad feeling between family members when something happens  Even an out-of-state parking ticket or a camera moving violation or toll-runner offense will fall to the registered owner's responsibility, ask me how I know.

Mike B.