Hi vorandhi W,
Welcome to the forum !!!
There is both options available for you either to hire private car & driver or choose Train journey. Between Delhi to Agra very good train operating called Gatimaan express and Agra fort station to Sawai Madhopur ( Ranthambore ) trains also available so now choice is yours.
Go My Journey
From delhi to Agra ...train Gatimaan express .
From agra to Ranthambore...there is both option ...by train from Agra fort to Ranthambore ( sawai madhopur railway station) or from bharatapur station to Ranthambore ( sawai madhopur)
Hire a private car to visit Ranthambore from Agra
Ranthambore Tiger Safari
As you have very less time, it will be too much of a travel for 2 nights.
Recommend you to read this blog for complete information on Sariska National Park. This will further help you to select the destination as per your liking.