Using multiple RTC libraries in one program
can I load several RTC libraries into my code and then use the functions I like from each one? 


It will depend on the libraries. Most likely they had some persistent variables, global to the routines, that help information exchange. If only some of the routines are used and others not, values in those variables may not be consistent.


  Will there be some conflict


That will depend on the way those libraries are implemented. No way of telling without seeing the code.

The point of doing this is a little bit suspect. It is not clear to me why you would want to have more than 1 RTC in an environment. If you are thinking about giving your program the option to function with multiple RTCs (but using one RTC at any given time), you can use either macro (at compile time) or wrap the RTCs in a logic layer (at run time).

For example, you can have a rtc_init() to reset different RTCs; and rtc_read() to return the time from the rtc. rtc_read() can be implemented based on which RTC is detected during initialization...