Don't talk to me about windows 10 ... I'm on my third level of MS support (previous levels being unable to solve the problem).
I know it's possible to do what you want, but I'm unsure exactly how to go about it. I think you can create a virtual machine within win10 on which you can run other versions or even Linux. Or I think you can create partitions on the hard drive and boot into each one separately at start up (I have Linux on my lap top and when it loaded on top of Win7 it created the partitions automatically).