So I've been going through and cleaning up the repository for you to just jump in and do the work. Although both files are functioning correctly, I would strongly suggest that both questions-funcs.php and questions.php migrate over to the twig framework.
It'll help keep the codebase cleaner, and fully utalise an excellent PHP framework.
src/admin/login.php is pretty much completely useless in its current state, any kind of user input will allow you to log into the administrator panel. Not really an issue with testing as dupe data was used, but for this to be used it requires proper functionality/security.
I discussed this with Hannah who suggested that we go down the .htaccess route, but obviously requirements may of changed.