Whenever I run apt I get a string of errors about a failed attempt to remove an old kernel. What should I do?
Make a backup from your personal datas. you have a somekind of typo in /etc/default/grub and not since today I think.
sudo mv /etc/default/grub /etc/default/grub.broken
Now we restore the file to default.
sudo cp -a /usr/share/grub/default/grub /etc/default/grub
this kernel versions are very old. I would make a clean install of an supported release like ubuntu 20.04