log into one of your droplets, go to /var/www. There will be a folder called ghost. just make a new directory called ghost2, and then navigate to inside that folder and then run the ghost install command.
Ghost will automatically set everything up and you just enter the domain details etc.
You can theoretically do this as much as you’d like IIRC, as long as each install is in it’s own folder and your VPS can handle it.