First of all, you have running two webservers:
- OSX's Apache on port 80
- Mediawiki's Apache on port 8080
3) It depends. If httpd.conf is located at
/etc/ it belongs to OSX's Apache , if it is located under /Application/mediawiki, it belongs to Bitnami Stack. In the same way, /usr/bin/apachectl belong to OSX's Apache and /Application/mediawiki/apache2/bin/apachectl belongs to the stack.
2) It is possible to put Mediawiki on port 80, but only when you install it from zero, it's not possible to change once the stack is installed . Open a Terminal, and go to the DMG image mounted on /Volume/Mediawiki, then execute this command
The installer will run and if your port 80 it is not used by other program , it will use it to server Mediawiki's webserver . Remember to stop the OSX's one.
1) Maybe you've asked for OSX webserver instead the Mediawiki one?