For cases like this with a more detailed dot file, to get a root shell, I would use
sudo -s
If that works, you might add one line to your .bashrc
if you like a more detailed prompt: https://superuser.com/questions/866269/use-sudo-s-but-show-current-folder-name
I don’t and want the root prompt to be very different so I know I’m root and not my normal user as that saves pain for me if I forget to get out of root as soon as possible.
If you want an excellent tutorial on root shell for macOS - see https://scriptingosx.com/2018/04/demystifying-root-on-macos-part-2-the-sudo-command/