Karen is Correct yo can only take over the mortgage and ownership IF the current owners and lender has an assumable loan (these are not common here) or you can lease with option to purchase.
However as karen stated it would be best have this looked over and directed to a real estate attorney.
If you need further assistance please contact me at your convenience.
Coral Shores Realtt
954-240-3940 or firstname.lastname@example.org
I advise you to seek the advice of a real estate lawyer if you want to enter into a Rent-to-Own or Lease Purchase deal to make sure the contract is written to protect you.