Teaching English

This week I had my first class with adults. It was rlly awkward because I walked in and now I'm the youngest. It's not like when I teach the kids who are so willing to try and repeat words, when you say something to adults they jus sit there and stare at you. I had no idea what level anyone in the class has so I was doing very basic lessons. Later I find out half of the class can basically speak English and the other half can only say hello. How am I supposed to teach to that? Also I don't think I'm a great teacher for the advanced people because honestly I don't know proper grammatically correct English, I just know spoken English. I also cannot teach them grammar. I think they have probably had teachers better than me in the past. Just because I am a native speaker doesn't mean I'm a great teacher. I need to just stick to a basic level.