UART TO RS-232 convension
1) Using UART to RS232 chips is the only option in this case? Are
  there any alternative ways?


Of course, you can implement a level converter using discrete hardware. For instance, this site describes the following very simple circuit:



Please take care of the "operating notes".


  code wise do I need to change anything?


No.


  Can I directly put UART tx data to the receive pin of these chips?


Yes.