When your parents disrespect you in front of your children?

Not sure if anyone has dealt with a similar situation. My mother treating me like a child in front of my young son has been teaching him that I don't have any authority. We are in a tight situation that has us living back at home with my mother after two years of being on our own. I cannot afford to move out again at this time, we have to stay here for at least 6-9 months before I can even think about being able to afford to go elsewhere. I have a decent job that I cannot lose, unfortunately it's just good enough to not qualify for any government assistance. Rental prices on the west coast in my particular area are outrageous. So moving is not an option at this time. 
How can I deal with my mother? The way she speaks to me, in front of my young son, like I'm a child myself. Now anytime I say anything to my son, he has totally disregarded my word and it's beginning to feel like we have more of a sibling relationship rather than a mother son relationship