Obv dates are very important as rates vary so much.
Just taking a random week in November, a 2BD Tower Suite in Mirage is $500/night. a 2BDR in Elara is $368/night*, not using any codes. (That's not including tax, resort fee etc etc for all the hotel re-sellers out there..) You could get 2 rooms in the Mandarin Oriental or Cosmopolitan for the same, or even 2x 1BDR suites in Elara for pretty much the same.
If you didn't want to spend that much, then its pretty much definitely going to be 2x regular rooms somewhere.
* advanced purchase, plus tax, no mention of resort fee. If you get on well with your sister(!) that's not a bad deal for a decent suite in a decent location.
Obv you get the master bedroom if you are paying...