I concur with Norway on this. Dual boot Windows are sketchy and can be hard to maintain and rebuild if your hard drive fails. This is certainly true for mechanical drives, but I haven't tested multi-OS boots on SSDs as of yet. I'm busy enough with all the various Win10 installation failures, apps that don't work such as Win10 Mail, etc. to even begin fiddling around with multi-boot windows on SSDs. There are probably some other forums where you can investigate that more fully. My Win10 installs have been on SSD as stand alone OSes on 2 different computers; 1 desktop (Dell DimE520) and 1 laptop (Sony Vaio VGN-FW139E). So far, my Win10 single-OS boot setups work pretty good on both SSD and mechanical drives. Adding a 2nd OS boot complicates things, and adds a 2nd failure point to each computer you run like that. This may not matter to you and your Dad as home users, but it creates lot of problems in the business world.
Years ago back at IBM, we prohibited multi-boot OS configs in laptops of all 70 of our local field engineers since they constantly crashed and failed. Many engineers disagreed with me, so I finally wrote a policy to REVOKE company-issued laptops where the engineer installed a multi-boot OS config, and forced them to buy their own laptop from their pocketbook if they continued experimenting on company issued laptops. IBM Corporate agreed with my reasoning and instituted the policy to this day.
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