Hi again, reading your problem in more detail, it seems you have 2 disks connected to the laptop at the same time. The solution I came up with was for booting from only one disk connected to the laptop. 
So being a little 
and 
thinking about it more …
I would solve one problem at a time.
Disconnect your Win 10 disk and install Ubuntu as if it was the only system.
Once you can boot Linux by itself and you can boot Win 10 by it self …
then let’s work on dual boot.
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I don’t think it is a requirement, but if Win 10 is on a MBR disk, I would put Linux on a MBR disk. IMHO
And always be sure to have backup of your data / system.