This is an answer to your first question: See which Microsoft account the license is linked to.
There is no direct way to show to which account a digital license is bound to. The account device list of the Microsoft account cannot be trusted: If I add another (non admin) user with a Microsoft account to my machine, the name of the computer will be added in the device list of the new account, too. Certainly, the digital license of my computer is still bound to my (admin) account and not to the new user.
Therfore you have to check the list of digital licenses in every Microsoft account you own.
The only method I know to list digital licenses bound to a Microsoft account is to try to transfer them to a new, "unknown" hardware. "Unknown" means, that on this hardware Windows 10 has not been installed before. "Try" means just to begin the transfer process until the last step and not to finish the activation process.
This new, "unknown" hardware can be a real hardware (new mainboard) or a virtual hardware (e.g. VMware virtual machine). It's important to note that the fingerprint of this hardware shall not exist in the database of Micrsoft's activation servers. Otherwise the hardware will be activated automatically and you won't get a chance to transfer a different digital license to it because it already has a digital license. The transfer process won't get offered.
My method for Windows 10 b1607 is as follows:
- Create a new virtual machine (VM)
- Install Windows 10 without any product key (the edition does not matter, Home or Pro, x86 or x64)
- Try to activate the VM
- Enter the windows activation dialog where it is possible to transfer your digital licenses to this VM ("Troubleshoot", "I changed hardware on this device recently")
- Enter your Microsoft account credentials of the account which you want to check
- Now you get a list ("Reactivate Windows", "Select this device from below") of devices which are bound to your Microsoft account and which have a digital license and which are in the same "device class" as your current device (the VM). This device list is the first part of the whole list of digital licenses of the account. "Device classes" are e. g. laptops, standalone PCs or virtual machines. In my opinion virtual machines are separated in different device classes, too (VMware, Oracle, etc.)
- To see the second part of the list of your digital licenses you have to list all devices which do not match the current VM, i.e. which belong to a different device class. Click on the link at the bottom of this page: "See other devices linked to your Microsoft account". Now you get the second part of the list of your digital licenses which belong to devices that cannot be transferred ("Device type does not match", Edition does not match")
This whole process seems to be reliable in respect to list my own digital licenses which I bound to different Microsoft accounts. However, some devices of the second list ("We can't reactivate Windows from these devices" ) migrated after some days to the first list ("devices which can be activated"). But this does not matter as the device entries stay the same.
And of course there is no guarantee that devices which are shown in the first list can be reactivated with the device with which you are currently checking the license. E.g. when I check with my virtual machine I also get some digital licenses in the first list which belong to a different device class (e.g. standalone PC). I am sure that a transfer from a license like this to a VM would not work in reality.