how Active directory in DR site

Hello

         I have two datacenter (1 DC, 1 DR) , current I have two server for root domain and two server child domain IN DC site , now I want install one root and one child DC in DR site , Current in active directory only one site (default first site) ,

- So if install in DR site I need must divide site ?

- and DC site and DR site I can use same subnet for AD server ?

Thanks