If you need help on turning off responsive function, you can have a look at the suggestion posted here. Although it is for my earlier theme, the same code changes apply in the case of Extinct too –
You may still need to manually adjust a few things to perfect it since theme was not built with non-responsive layout in mind.
For the menu, if you can leave a private message here with the URL, I can take a look. Will help if you specify how you would like it function/look.