Triple Boot Configuration |Installing Ubuntu on the same hard drive as Windows 7 and Windows 10

I am a lab facilitator at a community college in NC and we have recently upgraded our lab. We have been working to configure the lab in a way that would most effectively benefit the students. Currently all of the lab computers have Windows 7 and 10 installed in a dual boot configuration. We would like to add Ubuntu on a third partition and still be able to boot into Windows 7 and 10. I have access to a test machine so all suggestions are welcome and will be applied without the risk of breaking anything important :).

I've been installing the OSes in the following order:

1. Windows 7


2. Windows 10


3. Ubuntu

After install GRUB takes over as the bootloader and Windows 10 is an option. I select Windows 10 and it takes me to Windows 10's metro bootloader which gives me the option to boot into Windows 7. Selecting Win 7 brings me into Ubuntu.I ran update-grub and it broke Windows 10's bootloader. I know it broke the bootloader because now when I select the Win 10 option in GRUB im taken right into Windows 7. Please let me know if any of you all have any suggestions or recommendations that may solve this issue.

Thank you,
Robert

Ps. We do have Vmware installed as well so students can access Ubuntu in a virtual environment but we would like to have it on bare metal.

Did you create empty space using windows disk management tool in the second windows system? Did you turn off the fast-boot option in windows (Control Panel > Power options > turn off sleep/hibernate options then try to find a link 'adjust options currently unavailable' which will appear at the bottom of the page - you may need to scroll down)? Did you try to install ubuntu in legacy mode?

Here are some guidelines. During the installation (of ubuntu) process, select 'do something else' when options including 'install ubuntu alongside windows' are offered. Select the empty space created in windows (you may have to double-click on it). Format it as ext4, and define it as / (= root) partition. Install grub to sda (not sda1 etc).

At some stage there will be a message 'it appears that there are other operating systems not using UFI - if you proceed they may not work'. You may need return to previous screens to sort matters. Good luck, aarn