18 plants, 1 apartment? Yea, folks are smelling that shit. You probably don't even realize how far the smell is carrying since you are in the apartment with it and have become desensitized. It's like my house with smoking cigs. I haven't smoked inside for over 10 years, I started smoking inside last year, at first, I was like..holy hells, this reeks! Now, I think I've got the odor under control and my sister visits and she is like, damn your place smells like smoke. Funny part is, when I go visit my gal pal's mother, I can't stand the smoke smell in her house(different brand) but I can't smell it in mine because I'm used to it.
As far as your "watchers", go out there one night, don't say a word, don't even acknowledge them, go stand in the area they are, then start watching in the same direction they are watching. Just stand there statue still and silent until one of them breaks up the awkwardness and ask you what the hell you doing. Then just look over at them and casually say, "I was just curious what was so fucking interesting." And clam the hell back up.