1) I did not get the first question – I thought responsive function disabling is targeted towards the mobile devices only. Pls clarify.
2) For zooming out, can you try removing this line from the header.php line number 18 (or tweak it a bit to see how the browser behaves) and retry? –
If that does not help, can you pls post a private message here with the URL so that I can have a look at the site. It will help a lot if you post a temp login as well so that I can make changes and test it. Thanks!