You won’t be able to install both Paratext 9.1 and 9.3 on the same machine. All of the Paratext 9 versions are belong to the same product from the installer’s point of view and only one can be installed at the same time. If you install Paratext 9.1, it will be uninstalled when Paratext 9.3 is installed.
I found the related issue in our backlog and added a comment to it to explain your situation. Others make the decision about priorities, so I don’t have a projected fix time.
anon758749