Install Kali and Ubuntu on External SSD

Hi everyone,

My laptop have a SSD installed Windows 8.1 and a HDD. Also I have an external SSD disk installed Ubuntu. When I want to work on Ubuntu, I boot Windows and click "Advanced Options For Startup", select "Ubuntu" disk and laptop boot Ubuntu. But, I want to install Kali and Ubuntu this external SSD. I installed Ubuntu succeeded but after install Kali, there is an error on grub for Kali. Kali install grub to /dev/sda/, /dev/sdc/ but I want to just /dev/sdc/ or not install. There was Ubuntu grub already.

If I select Kali Lınux on grub screen, there is an error: mount: mounting /dev/sdc3 on /root failed: No such file or directory.

While installing,

/dev/sdc/
sdc1 swap
sdc2 Ubuntu ext4 /
sdc3 Kali ext4 /

The device name may have change, you should try to find out what is the current device name maybe by looking into the config from the ubuntu os.