I suggest booting and then do what you did to get them to boot to a Windows 10 login screen.
Once you are at a WIndows 10 login as an admin permissions user.
Use the admin command line to repair the BCD file.
Type each of the following commands and press enter after each one:
Bootrec /fixMBR
bootrec /fixBoot
bootrec /rebuildBCD
type Exit to close the command line window.
That should resolve the issue.