Switching to an installed older Mac OS

I have two questions.
1.
If I install Parallels 15 on my OSX 10.13 volume, and I already use a bootable OSX 10.8 volume, can I get Parallels to boot the older Mac OS, WITHOUT having to re-install the older Mac OS? Currently I switch between the two operating systems by using System Preferences > Startup Disk. I have crucial apps that only work in the older OS.
2.
Assuming Parallels CAN launch OS 10.8 inside 10.13, should I create a special volume of the older OS just for Parallels, or will the existing 10.8 volume still work as a bootable volume using System Preferences > Startup Disk?

 

Hello @MarkF14 It is not possible for Parallels to recognize the macOS on another partition on the same HDD, however, as a workaround, please follow the below steps and see if it works:
1) Create an entire time machine backup of the required Mac OS
2) Create a virtual machine with the required Mac OS system (Mountain lion/Sierra)
3) connect the external time machine back up drive to the virtual machine ( https://kb.parallels.com/122993 )
4) Boot your Mac OS virtual machine from following the steps from the article https://kb.parallels.com/124181
5) Restore the Mac OS by following steps from the article https://support.apple.com/en-in/HT203981
Note: If you still find any issues performing the above migration steps please reach out to apple support.