Need help with 你们不是向着我的吗？
Actually, it can be a real sentence in oral Chinese. 

向 can become a verb. It has 2 possible meanings based on the situation. 

First one mean "face to ..". The sentence can become "are you all facing to me?". 

The other meaning "are you on my side"/"don't you support me". 

For your case, I think it probably be the second meaning.