Draw a brush completely surrounding the stuff you wanna select.

Right click 2d view -> select inside

Update #10
I change a lot of parts of the map because radiant is a fucker when you try to work with diagonal stuff. 

prob not, depending how you do it, easiest way would just be model swapping i guess,

however you did post the youtu.be link. You get that link if its literally just uploaded and isnt finished rendering to full quality, and has no preview or thumbnail

I want to add this in my map and I have a few questions on setup. I'm assuming I still have to add the 'adjacent zone' thing in nazi_zombie_MAPNAME.gsc. Correct me if i'm wrong. I also want to have more than one zone that is activated by touch. Would I keep the targetname the same and just change the 'script_flag' for each specific zone? Sorry if these questions are nooby Haven't really dealt with zones before.