If you install each OS independently, making sure it does not see an "active" partition (except the empty one you are installing it to), then each will have a vanilla set of boot files for that OS alone.
You can then boot each system by making the OS partition "active" and rebooting.
When each OS is on its own HDD, you can leave them all active and boot the one of your choice by overriding the BIOS boot device.
You also have the option of multi-booting by subsequently adding additional entries in the boot menu of whichever OS you deem to be "in control", chaining to each of the other OSs.
Thanks for that...my reason for asking was that one disc is a sata hard drive the others are ssds, one sata,, one Pcie..if I wanted to remove the sata hard drive I would have no way of booting into the others, if I understand what you are saying. As the sata hard drive was my original disc and all ops were not installed independently.
When booted into any OS check Disk Management for "system"
Disk Management flags have the following meanings
"boot" = "this is the system you're running"
"system" = "this is where I found the boot files for the currently running system"
"active" (on the first HDD in the BIOS boot sequence) = "this is where I started the search for the boot files"
"active" (on subsequent HDDs in the BIOS boot sequence) ="this is where I will look if I don't find something in the MBR on the first HDD"