Clashing subsites and pages

I asked this in the chat (apologizing for the duplication) but realized that perhaps it required a more thorough space here on the forum to solve the issue.

Wordpress Multisite allows us to create sites like and, if we set the Wordpress main site to and happen to create the Page with URL, how do we control Wordpress behaviour on how to prioritize where the visitor is being redirected?

Also, how do we prevent clashes between the blog (works fine) and the blog (does not work) which gives a 404 error despite all the database fields looking fine and the admin section being available?