Because Delphi is a Win32-only IDE, you only need to build and install RTC packages for the Win32 platform. You can NOT build Delphi packages for other platforms, because Delphi ONLY has design-time packages for the Win32 platform.
Unfortunately this approaches causes what I call "project DCU pollution". You are forced to recompile the RTC SDK from source in every project that uses it, and the DCUs from RTC end up in your project directory along with your project's DCUs.
I always try to install 3rd party components/libs so that the source files are only compiled once, leaving me with DCUs only in the folder related to the component. The way I usually approach this is to
install 3rd party components under Win32 for the IDE, then switch to Win64 and
compile them again to separate xxx/win64 directories.
I set up the appropriate Win32 and Win64 library paths and everything works great. No
"dcu pollution" in my projects.