Solution:
I think there are a couple of options:
1) You need to rename your controllers or controller methods so as not to conflict with the WP pages.
or
2) You configure your .htaccess to ignore all file name or folder requests and rewrite them as CI compatible queries.
Something on the order of
RewriteRule ^members/(.*?)$ /members/getMemberJSON/$1 [R]
Note: That’s totally untested, but just an example.